Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($)
|
3 Months Ended |
9 Months Ended |
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
| Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract] |
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|
|
|
| Derivative instruments designated as fair value hedges |
$ 0
|
$ 0
|
$ 0
|
$ 0
|
| Recognized gains (losses) from fair value hedges or related hedged transactions |
0
|
0
|
0
|
0
|
| Designated as Hedging Instrument | Cash Flow Hedges | Interest Rate |
|
|
|
|
| Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract] |
|
|
|
|
| Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net |
|
(100,000)
|
|
(200,000)
|
| Other Derivative Instruments | Electric Commodity |
|
|
|
|
| Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract] |
|
|
|
|
| Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities |
(2,500,000)
|
200,000
|
(200,000)
|
2,000,000
|
| Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) |
$ 2,200,000
|
$ 400,000
|
$ (100,000)
|
$ 3,700,000
|