Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	$ 287	$ 248
Equity mutual funds	5	4
Marketable securities	102	230
Derivative assets	5	9
Derivative liabilities	(13)	(22)
Corporate debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	65	134
U.S. government and agency debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	32	57
Asset-backed debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	21
Certificates of deposit
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	5	15
Municipal debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	3
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	153	223
Equity mutual funds	5	4
Derivative assets	0	0
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. government and agency debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Asset-backed debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Certificates of deposit
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Significant Other Observable Inputs (Level 2)
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	134	25
Equity mutual funds	0	0
Derivative assets	5	9
Derivative liabilities	(13)	(22)
Significant Other Observable Inputs (Level 2) | Corporate debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	65	134
Significant Other Observable Inputs (Level 2) | U.S. government and agency debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	32	57
Significant Other Observable Inputs (Level 2) | Asset-backed debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	21
Significant Other Observable Inputs (Level 2) | Certificates of deposit
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	5	15
Significant Other Observable Inputs (Level 2) | Municipal debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	3
Significant Unobservable Inputs (Level 3)
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	0	0
Equity mutual funds	0	0
Derivative assets	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) | Corporate debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Significant Unobservable Inputs (Level 3) | U.S. government and agency debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Significant Unobservable Inputs (Level 3) | Asset-backed debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Significant Unobservable Inputs (Level 3) | Certificates of deposit
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	0	0
Significant Unobservable Inputs (Level 3) | Municipal debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities	$ 0	$ 0