Pension and Postretirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Capitalized portion of defined benefit contribution percent	14.00%	10.00%	13.00%	10.00%
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension and Other Postretirement Benefits			$ 1.8
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	4.8	9.7	9.6
Expected return on plan assets	(6.5)	(6.8)	(13.0)	(13.6)
Amortization of:
Prior service benefit	0.0	0.0	0.0	0.0
Actuarial loss	4.4	4.8	8.8	9.6
Total amortization	4.4	4.8	8.8	9.6
Pension / postretirement costs (benefits)	2.8	2.8	5.5	5.6
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			4.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.0	0.0	0.1	0.1
Interest cost on projected benefit obligation	0.8	0.9	1.6	1.7
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of:
Prior service benefit	(1.1)	(3.7)	(2.2)	(7.4)
Actuarial loss	1.2	1.3	2.3	2.5
Total amortization	0.1	(2.4)	0.1	(4.9)
Pension / postretirement costs (benefits)	0.9	$ (1.5)	1.8	$ (3.1)
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