Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	$ 159	$ 573
Marketable securities, fair value	138	142
Derivative assets	6	5
Derivative liabilities	5	0
Corporate debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	92	87
U.S. government and agency debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	4	12
Asset-backed debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	17	20
Certificates of deposit [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	19	17
Municipal debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	6	6
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	138	549
Derivative assets	0	0
Derivative liabilities	0	0
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Corporate debt securities [Member]
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) [Member] | U.S. government and agency debt securities [Member]
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) [Member] | Asset-backed debt securities [Member]
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) [Member] | Certificates of deposit [Member]
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) [Member] | Municipal debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	0	0
Significant Other Observable Inputs (Level 2) [Member]
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	21	24
Derivative assets	6	5
Derivative liabilities	5	0
Significant Other Observable Inputs (Level 2) [Member] | Corporate debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	92	87
Significant Other Observable Inputs (Level 2) [Member] | U.S. government and agency debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	4	12
Significant Other Observable Inputs (Level 2) [Member] | Asset-backed debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	17	20
Significant Other Observable Inputs (Level 2) [Member] | Certificates of deposit [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	19	17
Significant Other Observable Inputs (Level 2) [Member] | Municipal debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	6	6
Significant Unobservable Inputs (Level 3) [Member]
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	0	0
Derivative assets	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | U.S. government and agency debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Asset-backed debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Certificates of deposit [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Municipal debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, fair value	$ 0	$ 0