Available-For-Sale Securities (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Less than 12 months
Fair Value	$ 132	$ 109
Unrealized Losses	3	3
12 months or more
Fair Value	50	59
Unrealized Losses	4	5
Total
Fair Value	182	168
Unrealized Losses	7	8
Asset-backed Securities
Less than 12 months
Fair Value	0	0
Unrealized Losses	0	0
12 months or more
Fair Value	21	20
Unrealized Losses	2	3
Total
Fair Value	21	20
Unrealized Losses	2	3
U.S. governmental agency mortgage-backed securities
Less than 12 months
Fair Value	122	84
Unrealized Losses	2	1
12 months or more
Fair Value	12	15
Unrealized Losses	0	0
Total
Fair Value	134	99
Unrealized Losses	2	1
Residential
Less than 12 months
Fair Value	0	0
Unrealized Losses	0	0
12 months or more
Fair Value	10	14
Unrealized Losses	1	1
Total
Fair Value	10	14
Unrealized Losses	1	1
Large capitalization value
Less than 12 months
Fair Value	10	25
Unrealized Losses	1	2
12 months or more
Fair Value	7	10
Unrealized Losses	1	1
Total
Fair Value	17	35
Unrealized Losses	$ 2	$ 3