Pension Benefits (Details) $ in Millions			12 Months Ended
	Aug. 12, 2016 USD ($)	May 12, 2016 USD ($)	Dec. 31, 2016 USD ($) employees	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Unrecognized Postretirement Benefit Costs Arising During the Year			$ 14.2	$ 3.0	$ (106.4)
Defined Contribution Plan, Cost Recognized			$ 8.4	7.8	7.3
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension Plan, Number of Participants and Beneficiaries | employees			9,200
Defined Benefit Pension Plans Active Employees | employees			1,800
Percentage of Compensation, Defined Benefit Plan Employee Contribution			3.00%
Employer Contributions			$ 9.0	0.0
Defined Benefit Plan, Funded Status of Plan			(72.7)	(90.3)
Pension Expense Recognized			(1.5)	25.6	8.3
Unrecognized Postretirement Benefit Costs Arising During the Year			0.7	1.9	(102.0)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax			$ 144.7	152.2
Amortization Period, Accumulated Unrecognized Pension Gain/Loss			24 years
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax			$ 0.0	0.4
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
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments			0.3	0.0	0.0
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded Status of Plan			25.4	30.4
Pension Expense Recognized			(1.0)	2.1	1.8
Unrecognized Postretirement Benefit Costs Arising During the Year			4.8	$ 1.5	$ (7.0)
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
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
Amortization Period, Accumulated Unrecognized Pension Gain/Loss		5 years
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax		$ 0.3
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