Available-For-Sale Securities (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost Basis	$ 211		$ 211
Due after one year through five years, Cost Basis	589		589
Due after five through ten years, Cost Basis	28		28
Due after ten years, Cost Basis	31		31
Due in one year or less, Fair Value	214		214
Due after one year through five years, Fair Value	611		611
Due after five years through ten years, Fair Value	29		29
Due after ten years, Fair Value	30		30
Cost Basis	1,303		1,303
Fair Value	1,335		1,335
Schedule of Available-for-sale Securities
Cost Basis	1,483		1,483		1,479
Available-for-sale securities, Fair Value	1,611		1,611		1,586
Available-for-sale Securities, Proceeds, Gains and Losses
Proceeds from the sale of available-for-sale securities	90	66	297	243
Gross gains from the sale of available-for-sale securities	2	1	4	4
Gross losses from the sale of available-for-sale securities	1	0	2	0
U.S. governmental agency mortgage-backed securities
Schedule of Available-for-sale Securities
Cost Basis	336		336		291
Available-for-sale securities, Fair Value	337		337		299
Residential
Schedule of Available-for-sale Securities
Cost Basis	21		21		26
Available-for-sale securities, Fair Value	21		21		25
Commercial
Schedule of Available-for-sale Securities
Cost Basis	87		87		117
Available-for-sale securities, Fair Value	$ 93		$ 93		$ 127