Notes to the consolidated financial statements of Aegon N.V.  Note 43 256 Movements during the year of the present value of the defined benefit obligations 2013 2012 At January 1 restated 6,276 5,855 Current year service cost 98 106 Interest expense 243 267 Remeasurements of the defined benefit obligations: - Actuarial gains and losses arising from changes in demographic assumptions 5 31 - Actuarial gains and losses arising from changes in financial assumptions (286) 312 Past service cost 1 (29) Contributions by plan participants 11 11 Benefits paid (266) (263) Net exchange differences (146) (14) At December 31 5,935 6,276 Movements during the year in plan assets for retirement benefit plans 2013 2012 At January 1 2,747 2,543 Interest income (based on discount rate) 109 115 Remeasurements of the net defined liability (asset) 281 194 Contributions by employer 34 48 Contributions by plan participants - - Benefits paid (154) (149) Net exchange differences (108) (4) At December 31 2,909 2,747 2013 2012 Breakdown of plan assets for retirement benefit plans Quoted Unquoted Quoted Unquoted Equity instruments 331 6 261 4 Debt instrument 322 471 343 514 Derivatives - 25 - 7 Investment funds 29 1,485 23 1,364 Structured securities - 6 - 6 Other 9 225 16 209 At December 31 690 2,219 643 2,104 Aegon USA Defined benefit plans are mainly operated by Aegon USA, Aegon the Netherlands and Aegon UK. The following sections contain  a general description of the plans in each of these subsidiaries and a summary of the principal actuarial assumptions applied in  determining the value of defined benefit plans. Aegon USA has defined benefit plans covering substantially all its employees that are qualified under the Internal Revenue Service  Code, including all requirements for minimum funding levels. The defined benefit plans are governed by the Board of Managers of  Aegon USA. The Board of Managers has the full power and discretion to administer the plan and to apply all of its provisions, including  such responsibilities as, but not limited to, developing the investment policy and managing assets for the plan, maintaining required  funding levels for the plan, deciding questions related to eligibility and benefit amounts, resolving disputes that may arise from plan  participants and for complying with the plan provisions, and legal requirements related to the plan and its operation. The benefits  are based on years of service and the employee’s eligible annual compensation. The plans provide benefits based on a traditional  final average formula or a cash balance formula (which defines the accrued benefit in terms of a stated account balance), depending  on the age and service of the plan participant. The defined benefit plans were unfunded by EUR 207 million at December 31, 2013  (2012: EUR 611 million unfunded). Investment strategies are established based on asset/liability studies by actuaries which are updated as they consider appropriate.  These studies, along with the investment policy, assist to develop the appropriate investment criteria for the plan, including asset  allocation mix, return objectives, investment risk and time horizon, benchmarks and performance standards and restrictions and  prohibitions. The overall goal is to maximize total investment returns to provide sufficient funding for the present and anticipated  Annual Report 2013