Securities with Unrealized Losses (Detail) - USD ($) $ in Millions		6 Months Ended		12 Months Ended
		Jun. 30, 2016		Dec. 31, 2015
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	[1]	$ 491		$ 13,682
Less than twelve months, Unrealized Losses	[2]	2		129
Twelve months or longer, Fair Value		407	[1]	999
Twelve months or longer, Unrealized Losses		2	[2]	38
Total, Fair Value	[1]	898		14,681
Total, Unrealized Losses	[2]	4		167
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		442		13,681
Less than twelve months, Unrealized Losses	[2]	2		129
Twelve months or longer, Fair Value		407		999
Twelve months or longer, Unrealized Losses		2	[2]	38
Total, Fair Value		849		14,680
Total, Unrealized Losses	[2]	4		167
Temporarily Impaired Securities | US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value				2,169
Less than twelve months, Unrealized Losses	[2]			14
Twelve months or longer, Fair Value				0
Twelve months or longer, Unrealized Losses				0
Total, Fair Value				2,169
Total, Unrealized Losses	[2]			14
Temporarily Impaired Securities | US Government Agencies Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		0		75
Less than twelve months, Unrealized Losses	[2]	0		0
Twelve months or longer, Fair Value		3		34
Twelve months or longer, Unrealized Losses		0	[2]	1
Total, Fair Value		3		109
Total, Unrealized Losses	[2]	0		1
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		438		11,434
Less than twelve months, Unrealized Losses	[2]	1		114
Twelve months or longer, Fair Value		398		958
Twelve months or longer, Unrealized Losses		2	[2]	36
Total, Fair Value		836		12,392
Total, Unrealized Losses	[2]	3		150
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	[2]	0		0
Twelve months or longer, Fair Value		6		7
Twelve months or longer, Unrealized Losses		0	[2]	1
Total, Fair Value		6		7
Total, Unrealized Losses	[2]	0		1
Temporarily Impaired Securities | Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value		4		3
Less than twelve months, Unrealized Losses	[2]	1		1
Twelve months or longer, Fair Value		0		0
Twelve months or longer, Unrealized Losses		0	[2]	0
Total, Fair Value		4		3
Total, Unrealized Losses	[2]	1		1
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	[1]	49		1
Less than twelve months, Unrealized Losses	[2]	0		0
Twelve months or longer, Fair Value		0	[1]	0
Twelve months or longer, Unrealized Losses		0	[2]	0
Total, Fair Value	[1]	49		1
Total, Unrealized Losses	[2]	0		0
Other Than Temporarily Impaired Securities [Member] | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	[1]	1		1
Less than twelve months, Unrealized Losses	[2]	0		0
Twelve months or longer, Fair Value		0	[1]	0
Twelve months or longer, Unrealized Losses		0	[2]	0
Total, Fair Value	[1]	1		1
Total, Unrealized Losses	[2]	0		$ 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	[1]	48
Less than twelve months, Unrealized Losses	[2]	0
Twelve months or longer, Fair Value	[1]	0
Twelve months or longer, Unrealized Losses	[2]	0
Total, Fair Value	[1]	48
Total, Unrealized Losses	[2]	$ 0

[1] OTTI securities AFS are impaired securities for which OTTI credit losses have been previously recognized in earnings.

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