Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	$ 4,652		$ 10,724
Less than twelve months, Unrealized Losses	16		436
Twelve months or longer, Fair Value	6,433		915
Twelve months or longer, Unrealized Losses	215		98
Total, Fair Value	11,085		11,639
Total, Unrealized Losses	231		534
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value			10,619
Less than twelve months, Unrealized Losses			434
Twelve months or longer, Fair Value			915
Twelve months or longer, Unrealized Losses			98
Total, Fair Value			11,534
Total, Unrealized Losses			532
Temporarily Impaired Securities | US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	385		1,036
Less than twelve months, Unrealized Losses	2	[1]	47
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	385		1,036
Total, Unrealized Losses	2		47
Temporarily Impaired Securities | US Government Agencies Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	8		398
Less than twelve months, Unrealized Losses	0	[1]	29
Twelve months or longer, Fair Value	615		264
Twelve months or longer, Unrealized Losses	31		28
Total, Fair Value	623		662
Total, Unrealized Losses	31		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
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
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	4,259		9,173
Less than twelve months, Unrealized Losses	14		358
Twelve months or longer, Fair Value	5,804		618
Twelve months or longer, Unrealized Losses	184		67
Total, Fair Value	10,063		9,791
Total, Unrealized Losses	198		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			105	[2]
Less than twelve months, Unrealized Losses			2	[2]
Twelve months or longer, Fair Value			0
Twelve months or longer, Unrealized Losses			0
Total, Fair Value			105	[2]
Total, Unrealized Losses			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			105	[2]
Less than twelve months, Unrealized Losses			2	[2]
Twelve months or longer, Fair Value			0
Twelve months or longer, Unrealized Losses			0
Total, Fair Value			105	[2]
Total, Unrealized Losses			$ 2	[2]

[1] Securities with 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.