Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	$ 1,511		$ 285
Less than twelve months, Unrealized Losses	6		0
Twelve months or longer, Fair Value	37		40
Twelve months or longer, Unrealized Losses	7		9
Total, Fair Value	1,548		325
Total, Unrealized Losses	13		9
Temporarily Impaired Securities | US Government Agencies Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	298		10
Less than twelve months, Unrealized Losses	3		0
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	298		10
Total, Unrealized Losses	3		0
Temporarily Impaired Securities | US States and Political Subdivisions Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	1		1
Less than twelve months, Unrealized Losses	0		0
Twelve months or longer, Fair Value	24		28
Twelve months or longer, Unrealized Losses	5		4
Total, Fair Value	25		29
Total, Unrealized Losses	5		4
Temporarily Impaired Securities | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	1,212		224
Less than twelve months, Unrealized Losses	3		0
Twelve months or longer, Fair Value	0		1
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	1,212		225
Total, Unrealized Losses	3		0
Temporarily Impaired Securities | Collateralized Debt Obligations [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value			50
Less than twelve months, Unrealized Losses			0
Twelve months or longer, Fair Value			0
Twelve months or longer, Unrealized Losses			0
Total, Fair Value			50
Total, Unrealized Losses			0
Temporarily Impaired Securities | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	0		0
Less than twelve months, Unrealized Losses	0		0
Twelve months or longer, Fair Value	13		11
Twelve months or longer, Unrealized Losses	2		5
Total, Fair Value	13		11
Total, Unrealized Losses	2		5
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	0	[1]	16	[1]
Less than twelve months, Unrealized Losses	0	[1]	1	[1]
Twelve months or longer, Fair Value	3	[1]	209	[1]
Twelve months or longer, Unrealized Losses	1	[1]	32	[1]
Total, Fair Value	3	[1]	225	[1]
Total, Unrealized Losses	1	[1]	33	[1]
Other Than Temporarily Impaired Securities [Member] | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	0	[1]	1	[1]
Less than twelve months, Unrealized Losses	0	[1]	0	[1]
Twelve months or longer, Fair Value	3	[1]	3	[1]
Twelve months or longer, Unrealized Losses	1	[1]	2	[1]
Total, Fair Value	3	[1]	4	[1]
Total, Unrealized Losses	1	[1]	2	[1]
Other Than Temporarily Impaired Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value			15	[1]
Less than twelve months, Unrealized Losses			1	[1]
Twelve months or longer, Fair Value			206	[1]
Twelve months or longer, Unrealized Losses			30	[1]
Total, Fair Value			221	[1]
Total, Unrealized Losses			31	[1]
Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	1,511		301
Less than twelve months, Unrealized Losses	6		1
Twelve months or longer, Fair Value	40		249
Twelve months or longer, Unrealized Losses	8		41
Total, Fair Value	1,551		550
Total, Unrealized Losses	$ 14		$ 42

[1] Includes OTTI securities for which credit losses have been recorded in earnings in current or prior periods.