Changes in Credit Losses on Debt Securities Excluding Perpetual Preferred Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Balance at beginning of period	$ 277		$ 319		$ 298		$ 358
Credit losses on securities not previously considered other-than-temporarily impaired	2		1		5		3
Decreases in expected cash flows on securities for which other-than-temporary impairment was previously recognized	13		8		32		21
Total other-than-temporary impairment on debt securities	15		9		37		24
Increases in expected cash flows			(3)		(14)		(20)
Realized losses	(4)	[1]	(19)	[1]	(33)	[1]	(55)	[1]
Credit losses on security sales and securities expected to be sold	(142)				(142)		(1)
Balance at end of period	$ 146		$ 306		$ 146		$ 306

[1] Primarily represents principal losses allocated to mortgage and asset-backed securities in the Company's portfolio under the terms of the securitization transaction documents.