Pension and Postretirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Capitalized portion of defined benefit contribution percent	13.00%	10.00%	13.00%	10.00%
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension and Other Postretirement Benefits			$ 3.3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 0.0	$ 0.0	0.0	$ 0.0
Interest cost on projected benefit obligation	4.9	4.9	14.6	14.5
Expected return on plan assets	(6.5)	(6.9)	(19.5)	(20.5)
Amortization of:
Prior service benefit	0.0	0.1	0.0	0.1
Actuarial loss	4.3	4.7	13.1	14.3
Total amortization	4.3	4.8	13.1	14.4
Pension / postretirement costs (benefits)	2.7	2.8	8.2	8.4
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	9.0		9.0
Payment for Pension and Other Postretirement Benefits			5.5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.1	0.1	0.2	0.2
Interest cost on projected benefit obligation	0.8	0.8	2.4	2.5
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of:
Prior service benefit	(1.2)	(3.7)	(3.4)	(11.1)
Actuarial loss	1.2	1.2	3.5	3.7
Total amortization	0.0	(2.5)	0.1	(7.4)
Pension / postretirement costs (benefits)	0.9	$ (1.6)	2.7	$ (4.7)
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	2.0		2.0
Non-Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	$ 2.0		$ 2.0