Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Examination [Line Items]
Income tax expense at U.S. federal rate									$ 59.5	$ 41.5	$ 48.5
Income tax expense at U.S. federal rate, percent									21.00%	21.00%	21.00%
State income taxes, net of federal income tax benefit									$ 9.5	$ 7.5	$ 7.4
State income taxes, net of federal income tax benefit, percent									3.40%	3.80%	3.20%
Impacts of Tax Reform Act									$ 0.0	$ 0.0	$ (2.3)
Impacts of Tax Reform Act, percent									0	0	(0.010)
Stock-based compensation activity									$ (4.9)	$ (2.2)	$ (2.6)
Stock-based compensation activity, percent									(1.70%)	(1.10%)	(1.10%)
Equity in net income of unconsolidated subsidiaries (including holding gains upon acquisition)									$ (13.8)	$ 0.3	$ 1.0
Holding gain upon acquisition of additional ownership of equity method investments, percent									(4.90%)	0.20%	0.40%
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent									2.70%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount									$ 7.6	$ 0.0	$ 0.0
Net change in valuation allowance related to non-U.S. deffered tax assets, primarily net operating losses									$ 2.7	$ (2.1)	$ (0.2)
Net change in valuation allowance related to non-U.S. deffered tax assets, primarily net operating losses, percent									1.00%	(1.10%)	(0.10%)
Difference between U.S. federal statutory and foreign tax rates									$ (0.1)	$ 1.1	$ 0.2
Difference between U.S. federal statutory and foreign tax rates, percent									0.00%	0.60%	0.10%
Foreign tax provisions (GILTI, FDII, and BEAT)									$ (2.7)	$ (1.4)	$ (3.7)
Foreign tax provisions (GILTI, FDII, and BEAT), percent									(1.00%)	(0.70%)	(1.60%)
Change in unrecognized tax benefits									$ 1.2	$ (0.9)	$ 1.0
Changes in unrecognized tax benefits, percent									0.40%	(0.50%)	0.40%
Other tax credits									$ (2.2)	$ (2.2)	$ (3.6)
Other tax credits, percent									(0.80%)	(1.10%)	(1.60%)
Other - net									$ 2.9	$ 4.0	$ 2.1
Other - net, percent									1.00%	2.00%	0.90%
Income tax expense	$ 19.1	$ 16.9	$ 15.2	$ 8.5	$ 9.1	$ 13.3	$ 11.7	$ 11.5	$ 59.7	$ 45.6	$ 47.8
Income tax expense, percent									21.10%	23.10%	20.70%