Investment Securities (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013 securities	Dec. 31, 2012 securities
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months	248	46
Number of securities, 12 months or more	7	4
Number of securities, total	255	50
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	$ 1,034	$ 100
Estimated Fair Value, 12 months or more	83	73
Estimated Fair Value, Total	1,117	173
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(33)	(1)
Gross Unrealized Losses, 12 months or more	(12)	(4)
Gross Unrealized Losses, Total	(45)	(5)
Ratio Of Fair Value To Amortized Cost Between Ninety And One Hundred Percent [Member]
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months	241	46
Number of securities, 12 months or more	3	4
Number of securities, total	244	50
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	994	100
Estimated Fair Value, 12 months or more	17	73
Estimated Fair Value, Total	1,011	173
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(28)	(1)
Gross Unrealized Losses, 12 months or more	(1)	(4)
Gross Unrealized Losses, Total	(29)	(5)
Ratio Of Fair Value To Amortized Cost Less Than Ninety Percent [Member]
Available For Sale Securities Continuous Unrealized Loss Position Qualitative Disclosure [Abstract]
Number of securities, less than 12 months	7	0
Number of securities, 12 months or more	4	0
Number of securities, total	11	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Estimated Fair Value, Less than 12 months	40	0
Estimated Fair Value, 12 months or more	66	0
Estimated Fair Value, Total	106	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(5)	0
Gross Unrealized Losses, 12 months or more	(11)	0
Gross Unrealized Losses, Total	$ (16)	$ 0