Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 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	2.5
Interest Cost	[1]	7.4	8.1
Expected Return on Plan Assets	[1]	(11.0)	(10.6)
Amortization of Prior Service Credits	[1]	0.0	0.0
Amortization of Net Loss	[1]	3.0	2.5
Net Periodic Benefit Cost		2.1	2.5
Employer Contributions to Defined Benefit Pension Plans - Common Stock Value			13.5
Employer Contributions to Defined Benefit Plans		15.0	1.7
Expected Future Employer Contributions in 2018		0.0
Other Postretirement [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service Cost		1.2	1.1
Interest Cost	[1]	1.8	1.9
Expected Return on Plan Assets	[1]	(2.7)	(2.6)
Amortization of Prior Service Credits	[1]	(0.4)	(0.5)
Amortization of Net Loss	[1]	0.2	0.1
Net Periodic Benefit Cost		0.1	0.0
Employer Contributions to Defined Benefit Plans		0.0	$ 0.0
Expected Future Employer Contributions in 2018		$ 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.