Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Components of Net Periodic Benefit Cost (Income) [Abstract]
Employer Contributions to Defined Benefit Pension Plans - Common Stock Value				$ 0.0	$ 13.5
Pension [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service Cost		$ 2.7	$ 2.6	8.2	7.7
Interest Cost	[1]	7.4	8.1	22.2	24.4
Expected Return on Plan Assets	[1]	(11.1)	(10.6)	(33.2)	(31.8)
Amortization of Prior Service Credits	[1]	0.0	0.0	0.0	0.0
Amortization of Net Loss	[1]	3.0	2.5	9.0	7.4
Net Periodic Benefit Cost (Income)		2.0	2.6	6.2	7.7
Employer Contributions to Defined Benefit Pension Plans - Common Stock Value					13.5
Employer Contributions to Defined Benefit Plans				15.0	1.7
Other Postretirement [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service Cost		1.2	1.1	3.7	3.3
Interest Cost	[1]	1.8	2.0	5.4	5.8
Expected Return on Plan Assets	[1]	(2.7)	(2.6)	(8.2)	(7.9)
Amortization of Prior Service Credits	[1]	(0.4)	(0.5)	(1.3)	(1.5)
Amortization of Net Loss	[1]	0.2	0.0	0.6	0.2
Net Periodic Benefit Cost (Income)		$ 0.1	$ 0.0	0.2	(0.1)
Employer Contributions to Defined Benefit Plans				$ 0.0	$ 0.0

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