Information Regarding Changes in Unrealized Gains and Losses from Investments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	$ 1,721	$ 1,068	$ 874
Debt Securities | Available-for-sale Securities
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	1,963	1,105	170
Debt Securities | Transferred to Held to Maturity Securities
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	(101)	(12)	(31)
Perpetual Securities | Available-for-sale Securities
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	(143)	(24)	736
Equity Securities
Changes in unrealized gains (losses):
Changes in unrealized gains (losses)	$ 2	$ (1)	$ (1)