Available-For-Sale Securities (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost Basis	$ 125		$ 125
Due after one year through five years, Cost Basis	496		496
Due after five through ten years, Cost Basis	149		149
Due after ten years, Cost Basis	45		45
Due in one year or less, Fair Value	127		127
Due after one year through five years, Fair Value	510		510
Due after five years through ten years, Fair Value	171		171
Due after ten years, Fair Value	43		43
Cost Basis	1,241		1,241
Fair Value	1,292		1,292
Available-for-sale Securities, Proceeds, Gains and Losses
Proceeds from the sale of available-for-sale securities	65	56	177	122
Gross gains from the sale of available-for-sale securities	1	1	3	2
Gross losses from the sale of available-for-sale securities	0	0	0	(1)
Schedule of Available-for-sale Securities
Cost Basis	1,402		1,402		1,375
Available-for-sale securities	1,493		1,493		1,447
U.S. governmental agency mortgage-backed securities
Schedule of Available-for-sale Securities
Cost Basis	266		266		297
Available-for-sale securities	278		278		310
Residential
Schedule of Available-for-sale Securities
Cost Basis	29		29		33
Available-for-sale securities	26		26		30
Commercial
Schedule of Available-for-sale Securities
Cost Basis	131		131		142
Available-for-sale securities	$ 137		$ 137		$ 145