Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, Fair value	$ 138	$ 286
Fair Value, Measurements, Recurring [Member]
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	284	159
Derivative Assets	3	4
Derivative liabilities	(9)	(8)
Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, Fair value	86	174
Fair Value, Measurements, Recurring [Member] | U.S. government and agency debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, Fair value	12	32
Fair Value, Measurements, Recurring [Member] | Asset-backed debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, Fair value	9	18
Fair Value, Measurements, Recurring [Member] | Certificates of deposit [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, Fair value	16	35
Fair Value, Measurements, Recurring [Member] | Municipal debt securities [Member]
Assets and liabilities measured at fair value on a recurring basis
Marketable securities, Fair value	15	27
Fair Value, Measurements, Recurring [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	257	128
Derivative Assets
Derivative liabilities
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents	27	31
Derivative Assets	3	4
Derivative liabilities	(9)	(8)
Fair Value, Measurements, Recurring [Member] | 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	86	174
Fair Value, Measurements, Recurring [Member] | 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	12	32
Fair Value, Measurements, Recurring [Member] | 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	9	18
Fair Value, Measurements, Recurring [Member] | 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	16	35
Fair Value, Measurements, Recurring [Member] | 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	15	27
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets and liabilities measured at fair value on a recurring basis
Cash equivalents
Derivative Assets
Derivative liabilities
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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