Marketable Securities - Summary of Marketable Securities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 105	$ 59
Unrealized Gains	0	1
Fair Value	105	60
U.S. government and agencies
Schedule of Available-for-sale Securities [Line Items]
Cost	27	7
Unrealized Gains	0	0
Fair Value	27	7
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Cost	30	11
Unrealized Gains
Fair Value	30	11
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Cost	17	16
Unrealized Gains
Fair Value	17	16
Other securities
Schedule of Available-for-sale Securities [Line Items]
Cost	31	25
Unrealized Gains		1
Fair Value	$ 31	$ 26