Commitments and Contingencies Commitment and contingencies (additional information) (Details) (USD $)	1 Months Ended	3 Months Ended
Oct. 22, 2012	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2012 Maximum [Member]
Loss Contingencies [Line Items]
Payments to Acquire Interest in Joint Venture	$ 1,100,000,000
Nonoperating Gains (Losses)		$ 500,000,000	$ 700,000,000

The cash outflow associated with the investment in or advances to an entity in which the reporting entity shares control of the entity with another party or group.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3213-108585

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 17

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration