Investments (details) - Change in Net Unrealized Investment Gains (Losses) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Change in net unrealized investment gains (losses)
Change in net unrealized investment gains (losses)	$ 1,572	$ 5	$ 3,077
Fixed maturities [Member]
Change in net unrealized investment gains (losses)
Change in net unrealized investment gains (losses)	1,588	114	2,830
Equity securities [Member]
Change in net unrealized investment gains (losses)
Change in net unrealized investment gains (losses)	(2)	69	160
Other investments [Member]
Change in net unrealized investment gains (losses)
Change in net unrealized investment gains (losses)	$ (14)	$ (178)	$ 87