Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	$ 9,935		$ 10,724
Less than twelve months, Unrealized Losses	315		436
Twelve months or longer, Fair Value	915		915
Twelve months or longer, Unrealized Losses	78		98
Total, Fair Value	10,850		11,639
Total, Unrealized Losses	393		534
Temporarily Impaired Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	9,884		10,619
Less than twelve months, Unrealized Losses	315		434
Twelve months or longer, Fair Value	915		915
Twelve months or longer, Unrealized Losses	78		98
Total, Fair Value	10,799		11,534
Total, Unrealized Losses	393		532
Temporarily Impaired Securities | US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	1,252		1,036
Less than twelve months, Unrealized Losses	32		47
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	1,252		1,036
Total, Unrealized Losses	32		47
Temporarily Impaired Securities | US Government Agencies Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	352		398
Less than twelve months, Unrealized Losses	21		29
Twelve months or longer, Fair Value	269		264
Twelve months or longer, Unrealized Losses	22		28
Total, Fair Value	621		662
Total, Unrealized Losses	43		57
Temporarily Impaired Securities | US States and Political Subdivisions Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	11		12
Less than twelve months, Unrealized Losses	0		0
Twelve months or longer, Fair Value	0		20
Twelve months or longer, Unrealized Losses	0		2
Total, Fair Value	11		32
Total, Unrealized Losses	0		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	8,269		9,173
Less than twelve months, Unrealized Losses	262		358
Twelve months or longer, Fair Value	633		618
Twelve months or longer, Unrealized Losses	55		67
Total, Fair Value	8,902		9,791
Total, Unrealized Losses	317		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	13		13
Twelve months or longer, Unrealized Losses	1		1
Total, Fair Value	13		13
Total, Unrealized Losses	1		1
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than twelve months, Fair Value	51	[1]	105	[1]
Less than twelve months, Unrealized Losses	0		2	[1]
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	51	[1]	105	[1]
Total, Unrealized Losses	0		2	[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	51	[1]	105	[1]
Less than twelve months, Unrealized Losses	0		2	[1]
Twelve months or longer, Fair Value	0		0
Twelve months or longer, Unrealized Losses	0		0
Total, Fair Value	51	[1]	105	[1]
Total, Unrealized Losses	$ 0		$ 2	[1]

[1] Includes OTTI securities for which credit losses have been recorded in earnings in current or prior periods.