Asset Retirement Obligations (Changes In Company's Liability For Asset Retirement Obligations) (Details) - USD ($) $ in Millions |
3 Months Ended | |||
|---|---|---|---|---|
Mar. 31, 2016 |
Mar. 31, 2015 |
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| Asset Retirement Obligation [Abstract] | ||||
| Beginning Balance | $ 25.3 | $ 23.2 | ||
| Noncontributed net parent investment adjustments | [1] | 0.0 | (0.4) | |
| Accretion expense | 0.3 | 0.3 | ||
| Additions | 0.0 | 0.0 | ||
| Settlements | 0.0 | 0.0 | ||
| Change in estimated cash flows | (0.9) | 0.0 | ||
| Ending Balance | $ 24.7 | $ 23.1 | ||
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