Fair Value and Gross Unrealized Losses on Available-for-Sale Securities (Detail) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 930	$ 2,129	$ 326
Less than 12 months Unrealized Losses	(7)	(42)	(7)
12 months or more Fair Value	40	52	64
12 months or more Unrealized Losses	(3)	(5)	(9)
Total Fair Value	970	2,181	390
Total Unrealized Losses	(10)	(47)	(16)
US Treasury and Government
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value			150
12 months or more Fair Value		1	1
Total Fair Value		1	151
US States and Political Subdivisions Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value		11	2
12 months or more Fair Value	3	4	3
Total Fair Value	3	15	5
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	606	1,555	114
Less than 12 months Unrealized Losses	(4)	(32)	(1)
Total Fair Value	606	1,555	114
Total Unrealized Losses	(4)	(32)	(1)
Other Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	324	563	60
Less than 12 months Unrealized Losses	(3)	(10)	(6)
12 months or more Fair Value	37	47	60
12 months or more Unrealized Losses	(3)	(5)	(9)
Total Fair Value	361	610	120
Total Unrealized Losses	$ (6)	$ (15)	$ (15)