Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	$ 148	$ 125
Equity mutual funds	4	4
Marketable securities, fair value	82	154
Derivative assets	5	4
Derivative liabilities	21	26
Corporate debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	57	93
U.S. government and agency debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	2	22
Asset-backed debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	12	17
Certificates of deposit
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	9	18
Municipal debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	2	4
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	129	93
Equity mutual funds	4	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, fair value	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, fair value	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, fair value	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, fair value	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, fair value	0	0
Significant Other Observable Inputs (Level 2)
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	19	32
Equity mutual funds	0	0
Derivative assets	5	4
Derivative liabilities	21	26
Significant Other Observable Inputs (Level 2) | Corporate debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	57	93
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, fair value	2	22
Significant Other Observable Inputs (Level 2) | Asset-backed debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	12	17
Significant Other Observable Inputs (Level 2) | Certificates of deposit
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	9	18
Significant Other Observable Inputs (Level 2) | Municipal debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	2	4
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, fair value	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, fair value	0	0
Significant Unobservable Inputs (Level 3) | Asset-backed debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	0	0
Significant Unobservable Inputs (Level 3) | Certificates of deposit
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	0	0
Significant Unobservable Inputs (Level 3) | Municipal debt securities
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	$ 0	$ 0