Schedule of Gross Unrealized Losses and Fair Values of Securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investment [Line Items]
Less than 12 months, Fair Value	$ 332	$ 2,905
Less than 12 months, Gross Unrealized Losses	(3)	(118)
12 months or more, Fair Value	1,222	141
12 months or more, Gross Unrealized Losses	(40)	(9)
Total, Fair Value	1,554	3,046
Total, Gross Unrealized Losses	(43)	(127)
Debt Securities | Tax-exempt municipal securities
Investment [Line Items]
Less than 12 months, Fair Value	118	693
Less than 12 months, Gross Unrealized Losses	(2)	(28)
12 months or more, Fair Value	239	57
12 months or more, Gross Unrealized Losses	(5)	(5)
Total, Fair Value	357	750
Total, Gross Unrealized Losses	(7)	(33)
Debt Securities | Residential Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	4	6
12 months or more, Fair Value	2	1
12 months or more, Gross Unrealized Losses	(1)
Total, Fair Value	6	7
Total, Gross Unrealized Losses	(1)
Debt Securities | Commercial Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	106	270
Less than 12 months, Gross Unrealized Losses	(1)	(8)
12 months or more, Fair Value	192	40
12 months or more, Gross Unrealized Losses	(10)	(1)
Total, Fair Value	298	310
Total, Gross Unrealized Losses	(11)	(9)
Debt Securities | Asset-backed Securities
Investment [Line Items]
Less than 12 months, Fair Value		35
Less than 12 months, Gross Unrealized Losses		(1)
12 months or more, Fair Value	16
Total, Fair Value	16	35
Total, Gross Unrealized Losses		(1)
Debt Securities | Corporate Debt Securities
Investment [Line Items]
Less than 12 months, Fair Value	30	594
Less than 12 months, Gross Unrealized Losses		(28)
12 months or more, Fair Value	176	17
12 months or more, Gross Unrealized Losses	(6)	(2)
Total, Fair Value	206	611
Total, Gross Unrealized Losses	(6)	(30)
Debt Securities | U.S. Treasury And Other U.S. Government Corporations And Agencies | U.S. Treasury And Agency Obligations
Investment [Line Items]
Less than 12 months, Fair Value	38	231
Less than 12 months, Gross Unrealized Losses		(6)
12 months or more, Fair Value	92	5
12 months or more, Gross Unrealized Losses	(2)
Total, Fair Value	130	236
Total, Gross Unrealized Losses	(2)	(6)
Debt Securities | U.S. Treasury And Other U.S. Government Corporations And Agencies | Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	36	1,076
Less than 12 months, Gross Unrealized Losses		(47)
12 months or more, Fair Value	505	21
12 months or more, Gross Unrealized Losses	(16)	(1)
Total, Fair Value	541	1,097
Total, Gross Unrealized Losses	$ (16)	$ (48)