Financial Instruments - Schedule of Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	$ 612	$ 614
Short-Term Marketable Securities	118	47
Long-Term Marketable Securities	16	37
Cash	595	598
Cash, cash equivalents and marketable securities, Amortized Cost	746	698
Cash, cash equivalents and marketable securities, Fair Value	746	698
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	17	11
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	134	89
Fair Value	134	89
Cash and Cash Equivalents		5
Short-Term Marketable Securities	118	47
Long-Term Marketable Securities	16	37
Level 2 | U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	23	13
Fair Value	23	13
Short-Term Marketable Securities	21	9
Long-Term Marketable Securities	2	4
Level 2 | US treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	8	16
Fair Value	8	16
Cash and Cash Equivalents		4
Short-Term Marketable Securities	8	12
Level 2 | Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	16	5
Fair Value	16	5
Short-Term Marketable Securities	15	4
Long-Term Marketable Securities	1	1
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	5	1
Fair Value	5	1
Short-Term Marketable Securities	5	1
Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	82	54
Fair Value	82	54
Cash and Cash Equivalents		1
Short-Term Marketable Securities	69	21
Long-Term Marketable Securities	$ 13	$ 32