Securities with Unrealized Losses (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		$ 13,682	$ 2,586
Less than twelve months, Unrealized Losses		129	8
Twelve months or longer, Fair Value		999	5,057
Twelve months or longer, Unrealized Losses		38	79
Total, Fair Value		14,681	7,643
Total, Unrealized Losses		167	87
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		13,681	2,517
Less than twelve months, Unrealized Losses		129	7
Twelve months or longer, Fair Value		999	5,057
Twelve months or longer, Unrealized Losses		38	79
Total, Fair Value		14,680	7,574
Total, Unrealized Losses		167	86
Temporarily Impaired Securities | US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		2,169	150
Less than twelve months, Unrealized Losses		14	1
Twelve months or longer, Fair Value		0	0
Twelve months or longer, Unrealized Losses	[1]	0	0
Total, Fair Value		2,169	150
Total, Unrealized Losses		14	1
Temporarily Impaired Securities | US Government Agencies Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		75	20
Less than twelve months, Unrealized Losses	[1]	0	0
Twelve months or longer, Fair Value		34	132
Twelve months or longer, Unrealized Losses		1	2
Total, Fair Value		109	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		11,434	2,347
Less than twelve months, Unrealized Losses		114	6
Twelve months or longer, Fair Value		958	4,911
Twelve months or longer, Unrealized Losses		36	77
Total, Fair Value		12,392	7,258
Total, Unrealized Losses		150	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	[1]	0	0
Twelve months or longer, Fair Value		7	14
Twelve months or longer, Unrealized Losses		1	0	[1]
Total, Fair Value		7	14
Total, Unrealized Losses		1	0	[1]
Temporarily Impaired Securities | Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		3
Less than twelve months, Unrealized Losses		1
Twelve months or longer, Fair Value		0
Twelve months or longer, Unrealized Losses	[1]	0
Total, Fair Value		3
Total, Unrealized Losses		1
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	[2]	1	69
Less than twelve months, Unrealized Losses	[2]	0	1
Twelve months or longer, Fair Value		0	0
Twelve months or longer, Unrealized Losses		0	0
Total, Fair Value	[2]	1	69
Total, Unrealized Losses	[2]	0	1
Other Than Temporarily Impaired Securities [Member] | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	[2]	1
Less than twelve months, Unrealized Losses	[2]	0
Twelve months or longer, Fair Value		0
Twelve months or longer, Unrealized Losses		0
Total, Fair Value	[2]	1
Total, Unrealized Losses	[2]	$ 0
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	[2]		69
Less than twelve months, Unrealized Losses	[2]		1
Twelve months or longer, Fair Value			0
Twelve months or longer, Unrealized Losses			0
Total, Fair Value	[2]		69
Total, Unrealized Losses	[2]		$ 1

[1] Unrealized losses less than $0.5 million are presented as zero within the table.

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