Stockholders' Equity 1 (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Cash dividends
Declaration date	Feb. 07, 2013	Nov. 07, 2012	Aug. 02, 2012	May 08, 2012	Jan. 23, 2012	Nov. 09, 2011	Aug. 03, 2011	May 12, 2011
Dividend per share	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.05	$ 0.05	$ 0.05
Record date	Feb. 21, 2013	Nov. 20, 2012	Aug. 14, 2012	May 22, 2012	Feb. 14, 2012	Nov. 22, 2011	Aug. 16, 2011	May 23, 2011
Total amount	$ 114	$ 114	$ 116	$ 119	$ 117	$ 25	$ 25	$ 25	$ 463	$ 192	$ 82
Payment date	Mar. 19, 2013	Dec. 11, 2012	Sep. 11, 2012	Jun. 12, 2012	Mar. 13, 2012	Dec. 14, 2011	Sep. 14, 2011	Jun. 16, 2011

Aggregate dividends declared during the period for each share of common stock outstanding.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 32

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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