Pension Benefits (Details) $ in Millions			12 Months Ended
	Aug. 12, 2016 USD ($)	May 12, 2016 USD ($)	Dec. 31, 2017 USD ($) employees	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Unrecognized Postretirement Benefit Costs Arising During the Year			$ 3.9	$ 14.2	$ 3.0
Defined Contribution Plan, Cost Recognized			$ 10.6	8.4	7.8
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension Plan, Number of Participants and Beneficiaries | employees			9,000
Defined Benefit Pension Plans Active Employees | employees			1,600
Percentage of Compensation, Defined Benefit Plan Employee Contribution			3.00%
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax			$ 137.2	144.7
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax			$ 0.0	0.0
Defined Benefit Plan, Effect of Plan Amendment on Net Periodic Benefit Cost		$ 0.3
Defined Benefit Plan, Effect of Curtailment on Accumulated Unrecognized Pension Loss		23.3
Amortization Period, Accumulated Unrecognized Pension Gain/Loss			24 years
Employer Contributions			$ 0.0	9.0
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments			0.0	0.3	0.0
Defined Benefit Plan, Funded Status of Plan			(57.4)	(72.7)
Pension Expense Recognized			(7.7)	(1.5)	25.6
Unrecognized Postretirement Benefit Costs Arising During the Year			4.9	0.7	1.9
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Effect of Plan Amendment on Net Periodic Benefit Cost		1.3
Defined Benefit Plan, Effect of Curtailments on Projected Benefit Obligation		(5.2)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments			3.6
Defined Benefit Plan, Funded Status of Plan			26.3	25.4
Pension Expense Recognized			0.8	(1.0)	2.1
Unrecognized Postretirement Benefit Costs Arising During the Year			$ (1.6)	$ 4.8	$ 1.5
Post-Freeze [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax		$ 167.9
Amortization Period, Accumulated Unrecognized Pension Gain/Loss		25 years
Pre-Freeze [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax		$ 191.2
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax		$ 0.3
Amortization Period, Accumulated Unrecognized Pension Gain/Loss		5 years
Pre-Freeze [Member] | Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax		$ 1.6
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax		$ 1.3
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer Contributions	$ 9.0