Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Jointly Owned Utility Plant Interests [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	$ 0.0	$ 10.6	$ 0.1
Fixed-asset impairment (Note 14)	3.5	2.8	0.0
Estimated costs of removal	$ 143.6	$ 139.1	$ 132.8

The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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