Investments (details) - Change in Net Unrealized Investment Gains (Losses) - Rollforward (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) [Roll Forward]
Change in net unrealized investment gains (losses)	$ 1,572	$ 5	$ 3,077
Change in net unrealized investment gains (losses), tax expense	560	2	1,075
Change in net unrealized gain (loss) on investment securities, net of tax	1,012	3	2,002
Net unrealized gains (losses) on investment securities, balance, beginning of year	1,859	1,856	(146)
Net unrealized gains (losses) on investment securities, balance, end of year	$ 2,871	$ 1,859	$ 1,856