Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service Cost		$ 2.8	$ 2.7	$ 5.5	$ 5.3
Interest Cost	[1]	6.2	7.0	12.3	14.0
Expected Return on Plan Assets	[1]	(10.9)	(10.7)	(21.7)	(21.4)
Amortization of Prior Service Credits	[1]	(0.1)	(0.1)	(0.1)	(0.1)
Amortization of Net Loss	[1]	4.7	3.2	9.4	6.4
Net Periodic Benefit Cost (Credit)		2.7	2.1	5.4	4.2
Employer Contributions to Defined Benefit Plans				10.3	10.7
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year		0.0		0.0
Other Postretirement [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service Cost		0.9	0.9	1.8	1.7
Interest Cost	[1]	1.1	1.2	2.2	2.5
Expected Return on Plan Assets	[1]	(2.5)	(2.4)	(4.9)	(4.9)
Amortization of Prior Service Credits	[1]	(1.9)	(2.0)	(3.8)	(4.0)
Amortization of Net Loss	[1]	0.8	0.2	1.5	0.5
Net Periodic Benefit Cost (Credit)		(1.6)	$ (2.1)	(3.2)	(4.2)
Employer Contributions to Defined Benefit Plans				0.0	$ 0.0
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year		$ 0.0		$ 0.0

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