Labor Union Contracts (Details)	3 Months Ended
Mar. 31, 2012
Labor Union Contracts
Percentage of employees who are members of various bargaining units	40.00%
Employees covered under collective bargaining agreements \| Work force concentration
Labor Union Contracts
Percentage of concentration risk	73.00%
Number of employees covered under the agreement	14,000

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

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-Section 50

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

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-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant