Recent Accounting Pronouncements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Recent Accounting Pronouncements
Retained earnings	$ 6,617	$ 6,381
Accumulated other comprehensive income, net of tax	1,084	1,194
Total equity	9,617	9,712	9,749	9,694
Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts | Restatement for new accounting standard
Recent Accounting Pronouncements
Retained earnings				(1,400)
Accumulated other comprehensive income, net of tax				113
Total equity				$ (1,300)