Pension and Other Postretirement Benefit Plans Contributions by Plan Type (Details) $ in Millions	9 Months Ended
	Sep. 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	$ 57.6
Defined Benefit Plan, Plan Assets, Contributions by Employer	54.5
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	1.2
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