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Risk Management Activities and Derivative Transactions Derivatives Under FTP (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2013 | Sep. 30, 2013
--- | --- | ---
Derivative |  |
FTP transaction limit | $ 130 |
Maximum hedge volume | 75.00% |
Market value limitation of outstanding construction materials hedging transactions | 100 |
Portfolio value at risk limit for foreign currency transactions | 5 |
Swap contracts |  |
Derivative |  |
Remaining terms | 4 years |
Coal Contract Derivatives |  |
Derivative |  |
Fair value | $ 0 | $ 0

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