Recent Accounting Pronouncements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Restatement for new accounting standard	Dec. 31, 2010 Restatement for new accounting standard	Jan. 02, 2012 Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts Restatement for new accounting standard
Recent Accounting Pronouncements
Retained earnings	$ 5,845	$ 5,603		$ 4,770	$ (1,380)	$ (1,420)	$ 1,400
Accumulated other comprehensive income, net of tax	851	751		650	113	85	113
Total equity	$ 9,749	$ 9,694	$ 9,852	$ 9,950		$ (1,335)	$ (1,300)