Pension and Other Postretirement Benefit Plans Contributions by Plan Type (Details) $ in Millions	6 Months Ended
	Jun. 30, 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	15.5
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	0.9
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