Investments (Details 14) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Changes in fixed maturity securities with noncredit OTTI losses in accumulated other comprehensive income (loss)
Balance, beginning of period	$ (724)	$ (601)
Noncredit OTTI losses recognized	(29)	31
Securities sold with a previous noncredit OTTI loss	76	125
Subsequent increases in estimated fair value	(2)	(279)
Balance, end of period	$ (679)	$ (724)