Risk Management and Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011
Open fuel hedge position
Price Risk Derivatives, at Fair Value, Net	$ 135
Six Months Ended December 31, 2011 [Member]
Open fuel hedge position
Percentage of Projected Fuel Requirements Hedged	57.00%
Price Risk Derivatives, at Fair Value, Net	94
Year Ending December 31 2012 [Member]
Open fuel hedge position
Percentage of Projected Fuel Requirements Hedged	7.00%
Price Risk Derivatives, at Fair Value, Net	$ 41

Fair value as of the balance sheet date of price risk derivative assets, net of price risk derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized on the balance sheet.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 17
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13433-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13495-108611

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant