Regulatory Matters (Regulatory Liabilities) (Details) - USD ($)
$ in Millions |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
$ 310.9
|
|
| Cost Of Removal |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
153.5
|
|
| Regulatory Effects Of Accounting For Income Taxes |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
0.0
|
|
| Unrecognized Pension Benefit And Other Postretirement Benefit Costs |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
0.6
|
|
| Other Postretirement Costs |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
155.6
|
|
| Other Liabilities |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
$ 1.2
|
|
| Predecessor |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
|
$ 295.6
|
| Predecessor | Cost Of Removal |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
|
156.2
|
| Predecessor | Regulatory Effects Of Accounting For Income Taxes |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
|
10.9
|
| Predecessor | Unrecognized Pension Benefit And Other Postretirement Benefit Costs |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
|
8.3
|
| Predecessor | Other Postretirement Costs |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
|
117.3
|
| Predecessor | Other Liabilities |
|
|
| Regulatory Liabilities [Line Items] |
|
|
| Total Regulatory Liabilities |
|
$ 2.9
|