Investment Securities (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012 sec	Dec. 31, 2011 sec
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	$ 0	$ 15
Estimated Fair Value, 12 months or more	129	1,096
Estimated Fair Value, Total	129	1,111
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	0	(2)
Gross Unrealized Losses, 12 months or more	(7)	(73)
Gross Unrealized Losses, Total	(7)	(75)
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months	0	1
Number of securities, 12 months or more	14	136
Number of securities, total	14	137
Ratio Of Fair Value To Amortized Cost Between Ninety And One Hundred Percent [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	0	0
Estimated Fair Value, 12 months or more	126	884
Estimated Fair Value, Total	126	884
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	0	0
Gross Unrealized Losses, 12 months or more	(6)	(35)
Gross Unrealized Losses, Total	(6)	(35)
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months	0	0
Number of securities, 12 months or more	13	114
Number of securities, total	13	114
Ratio Of Fair Value To Amortized Cost Less Than Ninety Percent [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	0	15
Estimated Fair Value, 12 months or more	3	212
Estimated Fair Value, Total	3	227
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	0	(2)
Gross Unrealized Losses, 12 months or more	(1)	(38)
Gross Unrealized Losses, Total	$ (1)	$ (40)
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months	0	1
Number of securities, 12 months or more	1	22
Number of securities, total	1	23