Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	$ 2,586		$ 10,724
Less than twelve months, Unrealized Losses	8		436
Twelve months or longer, Fair Value	5,057		915
Twelve months or longer, Unrealized Losses	79		98
Total, Fair Value	7,643		11,639
Total, Unrealized Losses	87		534
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	2,517		10,619
Less than twelve months, Unrealized Losses	7		434
Twelve months or longer, Fair Value	5,057		915
Twelve months or longer, Unrealized Losses	79		98
Total, Fair Value	7,574		11,534
Total, Unrealized Losses	86		532
Temporarily Impaired Securities | US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	150		1,036
Less than twelve months, Unrealized Losses	1		47
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	150		1,036
Total, Unrealized Losses	1		47
Temporarily Impaired Securities | US Government Agencies Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	20		398
Less than twelve months, Unrealized Losses	0	[1]	29
Twelve months or longer, Fair Value	132		264
Twelve months or longer, Unrealized Losses	2		28
Total, Fair Value	152		662
Total, Unrealized Losses	2		57
Temporarily Impaired Securities | US States and Political Subdivisions Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value			12
Less than twelve months, Unrealized Losses			0	[1]
Twelve months or longer, Fair Value			20
Twelve months or longer, Unrealized Losses			2
Total, Fair Value			32
Total, Unrealized Losses			2
Temporarily Impaired Securities | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	2,347		9,173
Less than twelve months, Unrealized Losses	6		358
Twelve months or longer, Fair Value	4,911		618
Twelve months or longer, Unrealized Losses	77		67
Total, Fair Value	7,258		9,791
Total, Unrealized Losses	83		425
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	14		13
Twelve months or longer, Unrealized Losses	0	[1]	1
Total, Fair Value	14		13
Total, Unrealized Losses	0	[1]	1
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	69	[2]	105	[2]
Less than twelve months, Unrealized Losses	1	[2]	2	[2]
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	69	[2]	105	[2]
Total, Unrealized Losses	1	[2]	2	[2]
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	69	[2]	105	[2]
Less than twelve months, Unrealized Losses	1	[2]	2	[2]
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	69	[2]	105	[2]
Total, Unrealized Losses	$ 1	[2]	$ 2	[2]

[1] Unrealized losses less than $0.5 million are shown as zero.

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