Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	$ 8,708		$ 1,511
Less than twelve months, Unrealized Losses	385		6
Twelve months or longer, Fair Value	33		40
Twelve months or longer, Unrealized Losses	3		8
Total, Fair Value	8,741		1,551
Total, Unrealized Losses	388		14
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	8,645		1,511
Less than twelve months, Unrealized Losses	384		6
Twelve months or longer, Fair Value	33		37
Twelve months or longer, Unrealized Losses	3		7
Total, Fair Value	8,678		1,548
Total, Unrealized Losses	387		13
Temporarily Impaired Securities | US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	569
Less than twelve months, Unrealized Losses	22
Twelve months or longer, Fair Value	0
Twelve months or longer, Unrealized Losses	0
Total, Fair Value	569
Total, Unrealized Losses	22
Temporarily Impaired Securities | US Government Agencies Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	670		298
Less than twelve months, Unrealized Losses	38		3
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	670		298
Total, Unrealized Losses	38		3
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	20		24
Twelve months or longer, Unrealized Losses	2		5
Total, Fair Value	21		25
Total, Unrealized Losses	2		5
Temporarily Impaired Securities | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	7,405		1,212
Less than twelve months, Unrealized Losses	324		3
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	7,405		1,212
Total, Unrealized Losses	324		3
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		13
Twelve months or longer, Unrealized Losses	1		2
Total, Fair Value	13		13
Total, Unrealized Losses	1		2
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	63	[1]	0
Less than twelve months, Unrealized Losses	1	[1]	0
Twelve months or longer, Fair Value	0		3	[1]
Twelve months or longer, Unrealized Losses	0		1	[1]
Total, Fair Value	63	[1]	3	[1]
Total, Unrealized Losses	1	[1]	1	[1]
Other Than Temporarily Impaired Securities [Member] | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value			0
Less than twelve months, Unrealized Losses			0
Twelve months or longer, Fair Value			3	[1]
Twelve months or longer, Unrealized Losses			1	[1]
Total, Fair Value			3	[1]
Total, Unrealized Losses			1	[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	63	[1]
Less than twelve months, Unrealized Losses	1	[1]
Twelve months or longer, Fair Value	0
Twelve months or longer, Unrealized Losses	0
Total, Fair Value	63	[1]
Total, Unrealized Losses	$ 1	[1]

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