Available-For-Sale Securities (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Jun. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost Basis	$ 141		$ 141
Due after one year through five years, Cost Basis	530		530
Due after five through ten years, Cost Basis	135		135
Due after ten years, Cost Basis	44		44
Due in one year or less, Fair Value	143		143
Due after one year through five years, Fair Value	551		551
Due after five years through ten years, Fair Value	157		157
Due after ten years, Fair Value	43		43
Cost Basis	1,289		1,289
Fair Value	1,350		1,350
Schedule of Available-for-sale Securities
Cost Basis	1,451		1,451		1,375
Available-for-sale securities, Fair Value	1,561		1,561		1,447
Available-for-sale Securities, Proceeds, Gains and Losses
Proceeds from the sale of available-for-sale securities	66	58	243	180
Gross gains from the sale of available-for-sale securities	1	1	4	3
Gross losses from the sale of available-for-sale securities	0	0	0	1
U.S. governmental agency mortgage-backed securities
Schedule of Available-for-sale Securities
Cost Basis	288		288		297
Available-for-sale securities, Fair Value	298		298		310
Residential
Schedule of Available-for-sale Securities
Cost Basis	28		28		33
Available-for-sale securities, Fair Value	27		27		30
Commercial
Schedule of Available-for-sale Securities
Cost Basis	123		123		142
Available-for-sale securities, Fair Value	$ 131		$ 131		$ 145