Schedule Of Gross Unrealized Losses And Fair Values Of Securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Investment [Line Items]
Less than 12 months, Fair Value	$ 663	$ 625
Less than 12 months, Gross Unrealized Losses	(10)	(11)
12 months or more, Fair Value	84	135
12 months or more, Gross Unrealized Losses	(3)	(6)
Total, Fair Value	747	760
Total, Gross Unrealized Losses	(13)	(17)
Debt Securities | Tax-exempt municipal securities
Investment [Line Items]
Less than 12 months, Fair Value	100	53
Less than 12 months, Gross Unrealized Losses	(1)	0
12 months or more, Fair Value	26	48
12 months or more, Gross Unrealized Losses	(1)	(2)
Total, Fair Value	126	101
Total, Gross Unrealized Losses	(2)	(2)
Debt Securities | Residential Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	0	3
Less than 12 months, Gross Unrealized Losses	0	0
12 months or more, Fair Value	22	24
12 months or more, Gross Unrealized Losses	(1)	(2)
Total, Fair Value	22	27
Total, Gross Unrealized Losses	(1)	(2)
Debt Securities | Commercial Mortgage-Backed Securities
Investment [Line Items]
Less than 12 months, Fair Value	9	14
Less than 12 months, Gross Unrealized Losses	0	0
12 months or more, Fair Value	0	0
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	9	14
Total, Gross Unrealized Losses	0	0
Debt Securities | Asset-backed securities
Investment [Line Items]
Less than 12 months, Fair Value	10	16
Less than 12 months, Gross Unrealized Losses	0	0
12 months or more, Fair Value	0	4
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	10	20
Total, Gross Unrealized Losses	0	0
Debt Securities | Corporate Debt Securities
Investment [Line Items]
Less than 12 months, Fair Value	206	355
Less than 12 months, Gross Unrealized Losses	(9)	(10)
12 months or more, Fair Value	14	41
12 months or more, Gross Unrealized Losses	0	(1)
Total, Fair Value	220	396
Total, Gross Unrealized Losses	(9)	(11)
Debt Securities | U.S. Treasury And Other U.S. Government Corporations And Agencies | US Treasury And Agency Obligations
Investment [Line Items]
Less than 12 months, Fair Value	94	117
Less than 12 months, Gross Unrealized Losses	0	0
12 months or more, Fair Value	0	0
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	94	117
Total, Gross Unrealized Losses	0	0
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	244	67
Less than 12 months, Gross Unrealized Losses	0	(1)
12 months or more, Fair Value	22	18
12 months or more, Gross Unrealized Losses	(1)	(1)
Total, Fair Value	266	85
Total, Gross Unrealized Losses	$ (1)	$ (2)