52 Stress tests AEGON’s liquidity position in 2010 AEGON also has access to domestic and international  money markets through its USD 4.5 billion commercial  paper programs. At the end of 2010, AEGON had  EUR 701 million outstanding under these programs.  Liquidity is measured and stress-tested consistently  across the company, and a liquidity stress management  plan is maintained at Corporate Treasury and at  individual country units. Stress tests combine a “severe  surrender” scenario with an “impaired asset” scenario.  AEGON’s liquidity policy requires that all operating units  measure the period they can maintain a projected  positive cash balance without needing to sell any non- cash assets, while meeting all cash demands for a period  of two years$^{ 1}$. AEGON maintains back-up credit facilities with  international lenders to support outstanding amounts  under these commercial paper programs. The company’s  principal arrangement is a USD 5 billion syndicated  facility consisting of a USD 3 billion back-up credit  facility which matures in 2012 and a USD 2 billion  revolving letter of credit facility of which USD 1.5 billion  matures in 2015 and USD 0.5 billion matures in 2017.  In addition, AEGON also maintains USD 425 million of  shorter-dated bilateral back-up facilities. AEGON N.V.  has not drawn any amounts under any of its liquidity  back-up facilities. At the end of 2010, AEGON N.V. held EUR 1.7 billion in  excess capital compared with EUR 1.4 billion last year.  This was invested in highly liquid money market assets. Though operational leverage is not considered part  of AEGON’s capital base, it is an important source of  liquidity and funding. Operational debt relates primarily  to mortgage warehousing and the funding of  US Regulation XXX and Guideline AXXX redundant  reserves. Despite volatile market conditions, AEGON  issued the following residential mortgage-backed  securities during 2010: AEGON’s excess liquidity is invested in highly liquid,  short-term assets in accordance with the company’s  internal risk management policies. AEGON believes its  working capital, backed by its external funding programs  and facilities, is ample for the company’s present  requirements. Operational leverage Debt funding and back-up facilities Most of AEGON’s debt is issued by AEGON N.V., the  parent company. A limited number of other AEGON  companies may also issue debt securities, but for the  most part these securities are guaranteed by AEGON N.V.  AEGON N.V. has regular access to international capital  markets under a USD 6 billion debt issuance program.  Access to US markets is made possible by a separate  US shelf registration.  July  2010 AEGON completed the sale of EUR 1.02 billion  in residential mortgage backed securities to  institutional investors.  September  2010 AEGON completed the sale of a further  EUR 842 million in residential mortgage- backed securities to institutional investors.  These securities were issued under the Dutch SAECURE  program and managed by AEGON Levensverzekering N.V.,  the company’s life insurance unit in the Netherlands.  1 Where cash is defined as cash, cash equivalents plus highly liquid securities issued by governments or entities fully and explicitly  guaranteed by governments in domestic denominations.