Securities with Unrealized Losses (Detail) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		$ 4,033	$ 2,586
Less than twelve months, Unrealized Losses		36	8
Twelve months or longer, Fair Value		1,026	5,057
Twelve months or longer, Unrealized Losses		24	79
Total, Fair Value		5,059	7,643
Total, Unrealized Losses		60	87
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		4,033	2,517
Less than twelve months, Unrealized Losses		36	7
Twelve months or longer, Fair Value		1,026	5,057
Twelve months or longer, Unrealized Losses		24	79
Total, Fair Value		5,059	7,574
Total, Unrealized Losses		60	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		33	20
Less than twelve months, Unrealized Losses		0	0	[1]
Twelve months or longer, Fair Value		35	132
Twelve months or longer, Unrealized Losses		1	2
Total, Fair Value		68	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		3,996	2,347
Less than twelve months, Unrealized Losses		35	6
Twelve months or longer, Fair Value		982	4,911
Twelve months or longer, Unrealized Losses		23	77
Total, Fair Value		4,978	7,258
Total, Unrealized Losses		58	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		9	14
Twelve months or longer, Unrealized Losses	[1]	0	0
Total, Fair Value		9	14
Total, Unrealized Losses	[1]	0	0
Temporarily Impaired Securities | Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		4
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		4
Total, Unrealized Losses	[1]	1
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	[2]	0	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]	0	69
Total, Unrealized Losses	[2]	$ 0	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	[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] Includes OTTI securities AFS for which credit losses have been recorded in earnings in current or prior periods.