Asset Retirement Obligations (Changes In Company's Liability For Asset Retirement Obligations) (Details) - USD ($) $ in Millions |
6 Months Ended | ||||
|---|---|---|---|---|---|
Jun. 30, 2015 |
Jun. 30, 2014 |
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| Beginning Balance | $ 23.2 | ||||
| Noncontributed net parent investment adjustments | [1] | (0.4) | |||
| Accretion expense | 0.6 | ||||
| Additions | 0.4 | ||||
| Settlements | 0.0 | ||||
| Change in estimated cash flows | 0.0 | ||||
| Ending Balance | 23.8 | ||||
| Predecessor [Member] | |||||
| Beginning Balance | $ 23.2 | $ 26.3 | |||
| Noncontributed net parent investment adjustments | [1] | 0.0 | |||
| Accretion expense | 0.8 | ||||
| Additions | 2.0 | ||||
| Settlements | 0.0 | ||||
| Change in estimated cash flows | (0.2) | ||||
| Ending Balance | $ 28.9 | ||||
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