Investment Securities (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 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	$ 111	$ 15
Estimated Fair Value, 12 months or more	354	1,096
Estimated Fair Value, Total	465	1,111
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(2)	(2)
Gross Unrealized Losses, 12 months or more	(21)	(73)
Gross Unrealized Losses, Total	(23)	(75)
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months	15	1
Number of securities, 12 months or more	37	136
Number of securities, total	52	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	111	0
Estimated Fair Value, 12 months or more	281	884
Estimated Fair Value, Total	392	884
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(2)	0
Gross Unrealized Losses, 12 months or more	(8)	(35)
Gross Unrealized Losses, Total	(10)	(35)
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months	15	0
Number of securities, 12 months or more	31	114
Number of securities, total	46	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	73	212
Estimated Fair Value, Total	73	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	(13)	(38)
Gross Unrealized Losses, Total	$ (13)	$ (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	6	22
Number of securities, total	6	23