Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Fair Value Assets Measured on Recurring Basis Unobservable Input Reconciliation Asset
Level 3 measurement reconciliation, recurring basis, fair value assets beginning balance	$ 8	$ 16
Total unrealized gains included in other comprehensive income	1	1
Level 3 measurement reconciliation, recurring basis, fair value assets ending balance	9	17
Percentage of assets measured on recurring basis at fair value using significant unobservable inputs	0.20%
Auction rate securities
Fair Value Assets Measured on Recurring Basis Unobservable Input Reconciliation Asset
Level 3 measurement reconciliation, recurring basis, fair value assets beginning balance	8	16
Total unrealized gains included in other comprehensive income	1	1
Level 3 measurement reconciliation, recurring basis, fair value assets ending balance	$ 9	$ 17