Available-For-Sale Securities (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Available-For-Sale Securities
Due in one year or less, Cost Basis	$ 99
Due after one year through five years, Cost Basis	511
Due after five years through ten years, Cost Basis	145
Due after ten years, Cost Basis	46
Due in one year or less, Fair Value	101
Due after one year through five years, Fair Value	526
Due after five years through ten years, Fair Value	166
Due after ten years, Fair Value	44
Cost Basis	1,236
Fair Value	1,288
Available-for-sale Securities, Proceeds, Gains and Losses
Proceeds from the sale of available-for-sale securities	112	66
Gross gains from the sale of available-for-sale securities	2	1
Gross losses from the sale of available-for-sale securities		1
Schedule of Available-for-sale Securities.
Cost Basis	1,398		1,375
Fair Value	1,498		1,447
U.S. governmental agency mortgage-backed securities
Schedule of Available-for-sale Securities.
Cost Basis	266		297
Fair Value	279		310
Residential mortgage-backed securities
Schedule of Available-for-sale Securities.
Cost Basis	32		33
Fair Value	29		30
Commercial mortgage-backed securities
Schedule of Available-for-sale Securities.
Cost Basis	137		142
Fair Value	$ 143		$ 145