Commitments and Contingencies (Future Minimum Lease Payments) (Details) $ in Millions		12 Months Ended
	Mar. 01, 2019 USD ($) ft²	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Finance Lease, Right-of-Use Asset, Amortization		$ 10.3	$ 7.6
Finance Lease, Interest Expense		0.7	0.9
Operating Lease, Cost		62.7	59.7
Short-term Lease, Cost		4.0	4.3
Variable Lease, Cost		20.3	19.9
Lease, Cost		98.0	92.4
Finance Lease, Right-of-Use Asset		33.6	28.4
Right-of-use assets from operating leases		194.4	181.6
Finance Lease, Liability, Current		10.1	7.8
Finance Lease, Liability, Noncurrent		29.3	25.9
Current operating lease liabilities		55.0	52.7
Long-term operating lease liabilities		$ 142.8	$ 131.0
Finance Lease, Weighted Average Remaining Lease Term		4 years 3 months 18 days	4 years 10 months 24 days
Operating Lease, Weighted Average Remaining Lease Term		4 years 4 months 24 days	4 years 6 months
Finance Lease, Weighted Average Discount Rate, Percent		1.91%	2.71%
Operating Lease, Weighted Average Discount Rate, Percent		2.81%	3.69%
Operating Lease, Payments		$ 61.6	$ 58.1
Finance Lease, Principal Payments		10.8	6.4
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability		15.4	13.4
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		67.6	$ 51.5
Area of Leased Office Building | ft²	192,000
Purchase Price of Property at End of Lease Term	$ 41.2
Percentage of Lease Balance as Final Payment End of Lease Term	87.00%
Operating Leases
2018		59.8
2019		50.8
2020		43.3
2021		26.3
2022		13.4
Thereafter		16.8
Total minimum lease payments		210.4
Finance Leases
2018		10.5
2019		8.7
2020		5.8
2021		2.6
2022		0.8
Thereafter		11.8
Total minimum lease payments		40.2
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		(12.6)
Less imputed interest		(0.8)
Operating Lease, Liability		197.8
Present value of minimum payments		$ 39.4