Available-For-Sale Securities (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost Basis	$ 181
Due after one year through five years, Cost Basis	588
Due after five through ten years, Cost Basis	58
Due after ten years, Cost Basis	35
Due in one year or less, Fair Value	183
Due after one year through five years, Fair Value	618
Due after five years through ten years, Fair Value	65
Due after ten years, Fair Value	34
Cost Basis	1,323
Fair Value	1,377
Schedule of Available-for-sale Securities
Cost Basis	1,495		1,479
Available-for-sale securities, Fair Value	1,624		1,586
Available-for-sale Securities, Proceeds, Gains and Losses
Proceeds from the sale of available-for-sale securities	98	112
Gross gains from the sale of available-for-sale securities	1	2
Gross losses from the sale of available-for-sale securities	0	0
U.S. governmental agency mortgage-backed securities
Schedule of Available-for-sale Securities
Cost Basis	336		291
Available-for-sale securities, Fair Value	343		299
Residential
Schedule of Available-for-sale Securities
Cost Basis	24		26
Available-for-sale securities, Fair Value	24		25
Commercial
Schedule of Available-for-sale Securities
Cost Basis	101		117
Available-for-sale securities, Fair Value	$ 110		$ 127