Investments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale investments, balance sheet
Fair value	$ 406
Total short-term investments	416	360
Available-for-sale investments, maturities
Amortized cost, U.S. government agency securities due in 1 year or less	398
Amortized cost, Auction rate securities due after ten years	8
Amortized cost	406
Fair value, U.S. government agency securities due in 1 year or less	398
Fair value, Auction rate securities due after ten years	8
Fair value	406
U.S. government agency securities and corporate bonds \| Short-term investments.
Available-for-sale investments, balance sheet
Available-for-sale securities, debt maturities, amortized cost	387	344
Fair value	387	344
Available-for-sale investments, maturities
Fair value	387	344
Taxable auction rate securities
Available-for-sale investments, continuous unrealized loss position
Continuous unrealized loss position less than 12 months, unrealized losses		0
Continuous unrealized loss position less than 12 months, fair value		0
Continuous unrealized loss position 12 months or longer, unrealized losses		(1)
Continuous unrealized loss position 12 months or longer, fair value		16
Continuous unrealized loss position, aggregate unrealized losses		(1)
Continuous unrealized loss position, aggregate fair value		16
Corporate bonds \| Short-term investments.
Available-for-sale investments, balance sheet
Available-for-sale securities, debt maturities, amortized cost	11
Fair value	11
Available-for-sale investments, maturities
Fair value	11
Restricted cash \| Short-term investments.
Available-for-sale investments, balance sheet
Fair value	18	16
Available-for-sale investments, maturities
Fair value	18	16
Auction rate securities held through Morgan Stanley Smith Barney LLC \| Long-term investments.
Available-for-sale investments, balance sheet
Available-for-sale securities, debt maturities, amortized cost	8	17
Gross unrealized losses		(1)
Fair value	8	16
Available-for-sale investments, maturities
Fair value	$ 8	$ 16

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 7

-Footnote 2

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682