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Operations and Significant Accounting Policies - Reclassification of Prior Income Statement (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2016 | Sep. 30, 2016
Operating Revenue to Operating Revenue – Utility [Member] |  |
Reclassification of Prior Income Statement [Line Items] |  |
Prior Period Reclassification Amount | $ 253.3 | $ 740.5
Operating Revenue to Operating Revenue – Non-utility [Member] |  |
Reclassification of Prior Income Statement [Line Items] |  |
Prior Period Reclassification Amount | 96.3 | 257.7
Cost of Sales to Fuel, Purchased Power and Gas – Utility [Member] |  |
Reclassification of Prior Income Statement [Line Items] |  |
Prior Period Reclassification Amount | $ 0.7 | $ 4.6

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- Definition [Line Items] for Schedule of prior period reclassification adjustments to conform the presentation of prior period financial statements with the presentation in the current period. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition The amount of a reclassification adjustment made to prior period financial statement amounts. + References No definition available. + Details
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- Details
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- Details
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Period Type: |

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- Details
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Period Type: |