Pension and Other Postretirement Benefit Plans Contributions by Plan Type (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	$ 27.0
Defined Benefit Plan, Plan Assets, Contributions by Employer	4.1
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	2.4
Defined Benefit Plan, Plan Assets, Contributions by Employer	0.3
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	0.2
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 0.1