Supplemental Cash Flow Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
NON-CASH INVESTING AND FINANCING ACTIVITIES
Power plant long-term service agreement		$ (9.2)	$ (2.6)	$ 39.5
SUPPLEMENTAL CASH FLOW INFORMATION
Interest (net of interest capitalized)	[1]	153.8	139.6	141.9
Income taxes (net of income tax refunds)		2.8	(16.0)	(5.9)
Interest costs capitalized		$ 11.7	$ 18.0	$ 7.5

[1] Net of interest capitalized of $11.7 million, $18.0 million and $7.5 million in 2018, 2017 and 2016, respectively.