Pension Benefits - Changes in Fair Value of Pension Plans Level 3 (Details) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	$ 579.8	$ 520.9
Fair Value of Plan Assets at End of Year	525.3	579.8
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	0.3	0.4
Purchases, Sales and Settlements, Net	0.0	(0.1)
Fair Value of Plan Assets at End of Year	0.3	0.3
Receivables and Other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	(1.6)
Fair Value of Plan Assets at End of Year	1.3	(1.6)
Receivables and Other [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	0.3
Fair Value of Plan Assets at End of Year	$ 0.3	$ 0.3