Pension and Postretirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Capitalized portion of defined benefit contribution percent	12.00%	10.00%
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Contributions	$ 0.6
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.0	$ 0.0
Interest cost on projected benefit obligation	4.8	4.8
Expected return on plan assets	(6.5)	(6.8)
Amortization of:
Prior service benefit	0.0	0.0
Actuarial loss	4.4	4.8
Total amortization	4.4	4.8
Pension / postretirement costs (benefits)	2.7	2.8
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year			$ 9.0
Pension and Other Postretirement Benefit Contributions	2.0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.1	0.1
Interest cost on projected benefit obligation	0.8	0.8
Expected return on plan assets	0.0	0.0
Amortization of:
Prior service benefit	(1.1)	(3.7)
Actuarial loss	1.1	1.2
Total amortization	0.0	(2.5)
Pension / postretirement costs (benefits)	$ 0.9	$ (1.6)
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year			2.0
Non-Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year			$ 2.0