Changes in Equity and Comprehensive Income Changes in Equity and Comprehensive Income (Details of Accumulated Other Comprehensive Income Components) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income Tax Expense (Benefit)	$ 21.9	$ 15.7
Amounts reclassified from accumulated other comprehensive income	2.2
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	3.0	3.2
Income Tax Expense (Benefit)	0.8	0.6
Amounts reclassified from accumulated other comprehensive income	2.2	2.6
Pension Plan [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of prior service cost	(0.2)	(0.1)
Defined Benefit Plan, Amortization of Gain (Loss)	3.3	3.6
Other Postretirement Benefits Plan [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of prior service cost	0.0	0.0
Defined Benefit Plan, Amortization of Gain (Loss)	$ (0.1)	$ (0.3)