Asset Retirement Obligations (Changes In Company's Liability For Asset Retirement Obligations) (Details) - USD ($) $ in Millions |
12 Months Ended | ||||
|---|---|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
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| Beginning Balance | $ 23.2 | ||||
| Noncontributed net parent investment adjustments | [1] | (0.4) | |||
| Accretion expense | 1.2 | ||||
| Additions | 4.1 | ||||
| Settlements | 0.0 | ||||
| Change in estimated cash flows | 2.8 | ||||
| Ending Balance | 25.3 | $ 23.2 | |||
| Predecessor | |||||
| Beginning Balance | $ 23.2 | 26.3 | |||
| Noncontributed net parent investment adjustments | [1] | 0.0 | |||
| Accretion expense | 1.5 | ||||
| Additions | 2.2 | ||||
| Settlements | (6.6) | ||||
| Change in estimated cash flows | 0.2 | ||||
| Ending Balance | $ 23.2 | ||||
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