Recent Accounting Pronouncements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 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	$ 6,087	$ 5,603		$ 4,770	$ (1,380)	$ (1,420)	$ 1,400
Accumulated other comprehensive income, net of tax	1,267	751		650	113	85	113
Total equity	$ 9,821	$ 9,694	$ 9,737	$ 9,950	$ (1,267)	$ (1,335)	$ (1,300)