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Commitments, Guarantees and Contingencies - Coal, Rail and Shipping Contracts (Details) (Coal and Transportation [Member], USD $) In Millions, unless otherwise specified | Mar. 31, 2013
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Coal and Transportation [Member] |
Coal, Rail and Shipping Contracts [Line Items] |
Minimum Annual Payment Obligation, Current Year | $ 36.8
Minimum Annual Payment Obligation, Year Two | $ 1.3

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