Financial Instruments - Schedule of Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	$ 766	$ 614
Short-Term Marketable Securities	87	47
Long-Term Marketable Securities	38	37
Cash	740	598
Cash, cash equivalents and marketable securities, Amortized Cost	891	698
Cash, cash equivalents and marketable securities, Fair Value	891	698
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	18	11
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	133	89
Fair Value	133	89
Cash and Cash Equivalents	8	5
Short-Term Marketable Securities	87	47
Long-Term Marketable Securities	38	37
Level 2 | U.S. Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	29	13
Fair Value	29	13
Cash and Cash Equivalents	3
Short-Term Marketable Securities	26	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	12	16
Fair Value	12	16
Cash and Cash Equivalents	4	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	7	5
Fair Value	7	5
Short-Term Marketable Securities	7	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	5	1
Fair Value	5	1
Cash and Cash Equivalents	1
Short-Term Marketable Securities	4	1
Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	80	54
Fair Value	80	54
Cash and Cash Equivalents		1
Short-Term Marketable Securities	42	21
Long-Term Marketable Securities	$ 38	$ 32