Financial Instruments - Schedule of Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	$ 611	$ 614
Short-Term Marketable Securities	116	47
Long-Term Marketable Securities	29	37
Cash	604	598
Cash, cash equivalents and marketable securities, Amortized Cost	756	698
Cash, cash equivalents and marketable securities, Fair Value	756	698
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	4	11
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	148	89
Fair Value	148	89
Cash and Cash Equivalents	3	5
Short-Term Marketable Securities	116	47
Long-Term Marketable Securities	29	37
Level 2 | U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	25	13
Fair Value	25	13
Short-Term Marketable Securities	24	9
Long-Term Marketable Securities	1	4
Level 2 | US treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	5	16
Fair Value	5	16
Cash and Cash Equivalents		4
Short-Term Marketable Securities	5	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	16	4
Long-Term Marketable Securities		1
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	8	1
Fair Value	8	1
Cash and Cash Equivalents	3
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	94	54
Fair Value	94	54
Cash and Cash Equivalents		1
Short-Term Marketable Securities	66	21
Long-Term Marketable Securities	$ 28	$ 32