Financial Instruments - Schedule of Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	$ 887	$ 612
Short-Term Marketable Securities	17	118
Long-Term Marketable Securities	4	16
Cash	885	595
Cash, cash equivalents and marketable securities, Amortized Cost	908	746
Cash, cash equivalents and marketable securities, Fair Value	908	746
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1	17
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	22	134
Fair Value	22	134
Cash and Cash Equivalents	1
Short-Term Marketable Securities	17	118
Long-Term Marketable Securities	4	16
Level 2 | U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	3	23
Fair Value	3	23
Short-Term Marketable Securities	2	21
Long-Term Marketable Securities	1	2
Level 2 | US treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	2	8
Fair Value	2	8
Short-Term Marketable Securities	2	8
Level 2 | Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	1	16
Fair Value	1	16
Short-Term Marketable Securities	1	15
Long-Term Marketable Securities		1
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	1	5
Fair Value	1	5
Cash and Cash Equivalents	1
Short-Term Marketable Securities		5
Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	15	82
Fair Value	15	82
Short-Term Marketable Securities	12	69
Long-Term Marketable Securities	$ 3	$ 13