Financial Instruments - Schedule of Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 653	$ 614
Short-Term Marketable Securities	39	47
Long-Term Marketable Securities	17	37
Cash	623	598
Cash, cash equivalents and marketable securities, Amortized Cost	709	698
Cash, cash equivalents and marketable securities, Fair Value	709	698
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	29	11
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	57	89
Fair Value	57	89
Cash and cash equivalents	1	5
Short-Term Marketable Securities	39	47
Long-Term Marketable Securities	17	37
Level 2 | U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	10	13
Fair Value	10	13
Short-Term Marketable Securities	10	9
Long-Term Marketable Securities		4
Level 2 | US treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	6	16
Fair Value	6	16
Cash and cash equivalents		4
Short-Term Marketable Securities	6	12
Level 2 | Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	4	5
Fair Value	4	5
Short-Term Marketable Securities	2	4
Long-Term Marketable Securities	2	1
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	1	1
Fair Value	1	1
Cash and cash equivalents	1
Short-Term Marketable Securities		1
Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	36	54
Fair Value	36	54
Cash and cash equivalents		1
Short-Term Marketable Securities	21	21
Long-Term Marketable Securities	$ 15	$ 32