Preferred dividends accrued but not paid were $4 at the end of 2013. At December 31, 2014, we maintained cash balances of $22 on deposit with financial institutions to support surety bonds,  letters of credit and bank guarantees and to provide credit enhancements for certain lease agreements. Surety bonds enable us to  self-insure our workers compensation obligations.  We accrue the estimated liability for workers compensation claims, including  incurred but not reported claims. Accordingly, no significant impact on our financial condition would result if the surety bonds  were called. For a summary of litigation and other contingencies, see Note 15 to our consolidated financial statements in Item 8.  We  believe that any liabilities beyond the amounts already accrued that may result from these contingencies will not have a  material adverse effect on our liquidity, financial condition or results of operations. The preparation of our consolidated financial statements in accordance with U.S. generally accepted accounting principles  (GAAP) requires us to use estimates and make judgments and assumptions about future events that af fect the reported amounts  of assets, liabilities, revenue, expenses and the related disclosures. Considerable judgment is often involved in making these  determinations. Critical estimates are those that require the most dif ficult, subjective or complex judgments in the preparation  of the financial statements and the accompanying notes.  We evaluate these estimates and judgments on a regular basis.  We  believe our assumptions and estimates are reasonable and appropriate. However , the use of different assumptions could result in  significantly different results and actual results could dif fer from those estimates.  The following discussion of accounting  estimates is intended to supplement the Summary of Significant  Accounting Policies presented as Note 1 to our consolidated  financial statements in Item 8. Income taxes  — Accounting for income taxes is complex, in part because we conduct business globally and therefore file  income tax returns in numerous tax jurisdictions. Significant judgment is required in determining the income tax provision,  uncertain tax positions, deferred tax assets and liabilities and the valuation allowances recorded against our net deferred tax  assets. A valuation allowance is provided when, in our judgment based upon available information, it is more likely than not  that a portion of such deferred tax assets will not be realized.  To make this assessment, we consider the historical and projected  future taxable income or loss in dif ferent tax jurisdictions and we review our tax planning strategies.  We have recorded  valuation allowances against deferred tax assets in the U.S. and other foreign jurisdictions where realization has been  determined to be uncertain. Since future financial results may dif fer from previous estimates, periodic adjustments to our  valuation allowances may be necessary. At December 31, 2014, we continue to carry a valuation allowance against certain deferred tax assets in the U.S. because,  on a more likely than not basis, we have concluded that a significant portion of the U.S. deferred tax assets are not expected to  be realized. When evaluating the continued need for this valuation allowance we consider all components of comprehensive  income, and we weight the positive and negative evidence, putting greater reliance on objectively verifiable historical evidence  than on projections of future profitability that are dependent on actions that have not taken place as of the assessment date.  We  also consider the pro forma ef fects on historical profitability of actions that have occurred through the year of assessment and  objectively verifiable effects of material forecasted events that have a sustained ef fect on future profitability , as well as the  effect on historical profits of nonrecurring events.These effects included items such as the lost future interest income resulting  from the prepayment on and subsequent sale of the payment-in-kind callable note receivable and the additional interest expense  resulting from the $750 senior unsecured notes payable issued in July 2013.We also consider the pro forma historical and  prospective effects of tax planning strategies expected to be implemented. Our 2014 assessment considered the ef fects of  certain tax planning actions expected to be completed in 2015.  A sustained period of profitability , after giving pro forma ef fect  to implemented actions, planned actions and nonrecurring events, along with positive expectations for future profitability are  necessary for a determination that a valuation allowance should be released. In 2015, we expect to generate taxable income associated with certain tax planning actions.  The gain and related income  associated with these actions are estimated to generate tax of $179.  Although the actual gain and operating income may dif fer  from the current estimate, we concluded that they were objectively verifiable and reasonably estimated.  While our U.S.  operations have experienced improved profitability in recent years, our analysis of the income of the U.S. operations, as  adjusted for pro forma ef fects of developments through 2014 and planned future actions, demonstrates historical losses as of  December 31, 2014 with an uncertain forecast of near break-even results.Therefore, we have not achieved a level of sustained  profitability that would, in our judgment, support a release of the valuation allowance at December 31, 2014 beyond the $179  33 Critical Accounting Estimates Contingencies