Changes in Equity and Accumulated Other Comprehensive Loss (Details of Accumulated Other Comprehensive Income Components) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income Tax Expense (Benefit)	$ 18.8	$ 21.1	$ 40.4	$ 70.5
Amounts reclassified from accumulated other comprehensive income			10.4
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	4.4	3.9	13.5	10.2
Income Tax Expense (Benefit)	1.1	0.9	3.1	2.4
Amounts reclassified from accumulated other comprehensive income	3.3	3.0	10.4	7.8
Pension Plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of prior service cost	(0.1)	0.1	(0.2)	(0.3)
Defined Benefit Plan, Amortization of Gain (Loss)	4.8	4.8	14.5	11.5
Other Postretirement Benefits Plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of prior service cost	(0.3)	(0.8)	(0.8)	(0.8)
Defined Benefit Plan, Amortization of Gain (Loss)	$ 0.0	$ (0.2)	$ 0.0	$ (0.2)