Pension and Other Postretirement Benefit Plans - Components of Net Periodic Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service Cost		$ 4.7	$ 4.4	$ 3.9
Interest Cost	[1]	7.1	7.7	7.4
Expected Return on Plan Assets	[1]	(10.9)	(10.5)	(11.2)
Amortization of Loss	[1]	0.8	0.3	0.2
Amortization of Prior Service Cost	[1]	(2.1)	(2.0)	(2.9)
Net Pension Cost		(0.4)	(0.1)	(2.6)
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service Cost		11.0	10.2	8.1
Interest Cost	[2]	29.6	32.5	33.2
Expected Return on Plan Assets	[2]	(44.4)	(42.4)	(43.6)
Amortization of Loss	[2]	11.4	9.9	9.5
Amortization of Prior Service Cost	[2]	(0.1)	0.0	0.0
Net Pension Cost		$ 7.5	$ 10.2	$ 7.2

[1] These components of net periodic postretirement health and life cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.

[2] These components of net periodic pension cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.