Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	$ 2,453		$ 2,586
Less than twelve months, Unrealized Losses	10		8
Twelve months or longer, Fair Value	1,241		5,057
Twelve months or longer, Unrealized Losses	20		79
Total, Fair Value	3,694		7,643
Total, Unrealized Losses	30		87
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	2,386		2,517
Less than twelve months, Unrealized Losses	9		7
Twelve months or longer, Fair Value	1,241		5,057
Twelve months or longer, Unrealized Losses	20		79
Total, Fair Value	3,627		7,574
Total, Unrealized Losses	29		86
Temporarily Impaired Securities | US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value			150
Less than twelve months, Unrealized Losses			1
Twelve months or longer, Fair Value			0
Twelve months or longer, Unrealized Losses			0
Total, Fair Value			150
Total, Unrealized Losses			1
Temporarily Impaired Securities | US Government Agencies Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	47		20
Less than twelve months, Unrealized Losses	0	[1]	0	[1]
Twelve months or longer, Fair Value	52		132
Twelve months or longer, Unrealized Losses	1		2
Total, Fair Value	99		152
Total, Unrealized Losses	1		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	2,339		2,347
Less than twelve months, Unrealized Losses	9		6
Twelve months or longer, Fair Value	1,175		4,911
Twelve months or longer, Unrealized Losses	19		77
Total, Fair Value	3,514		7,258
Total, Unrealized Losses	28		83
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		14
Twelve months or longer, Unrealized Losses	0	[1]	0	[1]
Total, Fair Value	14		14
Total, Unrealized Losses	0	[1]	0	[1]
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	67	[2]	69	[2]
Less than twelve months, Unrealized Losses	1	[2]	1	[2]
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	67	[2]	69	[2]
Total, Unrealized Losses	1	[2]	1	[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	67	[2]	69	[2]
Less than twelve months, Unrealized Losses	1	[2]	1	[2]
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	67	[2]	69	[2]
Total, Unrealized Losses	$ 1	[2]	$ 1	[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.