Available-For-Sale Securities (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Less than 12 months
Fair Value	$ 29	$ 164
Unrealized Losses	2	8
12 months or more
Fair Value	50	53
Unrealized Losses	9	10
Total
Fair Value	79	217
Unrealized Losses	11	18
Corporate bonds
Less than 12 months
Fair Value		54
Unrealized Losses		1
12 months or more
Fair Value		1
Total
Fair Value		55
Unrealized Losses		1
Asset-backed securities
Less than 12 months
Fair Value	3	1
12 months or more
Fair Value	19	20
Unrealized Losses	4	5
Total
Fair Value	22	21
Unrealized Losses	4	5
U.S. governmental agency mortgage-backed securities
Less than 12 months
Fair Value		51
Unrealized Losses		1
Total
Fair Value		51
Unrealized Losses		1
Residential mortgage-backed securities
Less than 12 months
Fair Value	2	3
12 months or more
Fair Value	16	18
Unrealized Losses	3	3
Total
Fair Value	18	21
Unrealized Losses	3	3
Commercial mortgage-backed securities
Less than 12 months
Fair Value	4	15
12 months or more
Fair Value	8	8
Unrealized Losses	1	1
Total
Fair Value	12	23
Unrealized Losses	1	1
Large capitalization value
Less than 12 months
Fair Value	20	36
Unrealized Losses	2	5
12 months or more
Fair Value	7	6
Unrealized Losses	1	1
Total
Fair Value	27	42
Unrealized Losses	3	6
Smaller company growth
Less than 12 months
Fair Value		4
Unrealized Losses		1
Total
Fair Value		4
Unrealized Losses		$ 1