Commitments and Contingencies (Energy Purchase Commitments) (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended |
---|---|---|
Sep. 30, 2015 |
Sep. 30, 2015 |
|
Fuel | Loss on Long-term Purchase Contracts | ||
Loss Contingencies [Line Items] | ||
Coal contract modification charges | $ 41 | $ 41 |