Commitments and Contingencies (Future Minimum Lease Payments) (Details) $ in Millions		12 Months Ended
	Mar. 01, 2019 USD ($) ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Operating Lease Term	5 years
Finance Lease, Right-of-Use Asset		$ 28.4
Operating Lease, Right-of-Use Asset		181.6	$ 0.0
Finance Lease, Liability, Current		7.8
Finance Lease, Liability, Noncurrent		25.9
Operating Lease, Liability, Current		52.7	0.0
Operating Lease, Liability, Noncurrent		$ 131.0	0.0
Finance Lease, Weighted Average Remaining Lease Term		4 years 10 months 24 days
Operating Lease, Weighted Average Remaining Lease Term		4 years 6 months
Finance Lease, Weighted Average Discount Rate, Percent		2.71%
Operating Lease, Weighted Average Discount Rate, Percent		3.69%
Finance Lease, Right-of-Use Asset, Amortization		$ 7.6
Finance Lease, Interest Expense		0.9
Operating Lease, Cost		59.7
Short-term Lease, Cost		4.3
Variable Lease, Cost		19.9
Lease, Cost		92.4
Operating Lease, Payments		58.1
Finance Lease, Principal Payments		6.4
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability		13.4
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		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		58.4	47.4
2019		46.3	38.4
2020		33.8	27.2
2021		26.7	17.9
2022		17.0	12.7
Thereafter		17.1	16.1
Total minimum lease payments		199.3	159.7
Finance Leases
2018		8.4	6.6
2019		6.8	5.4
2020		4.9	3.8
2021		2.5	2.1
2022		0.6	0.9
Thereafter		11.7	12.8
Total minimum lease payments		34.9	31.6
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		(15.6)
Less imputed interest		(1.2)	(2.1)
Operating Lease, Liability		183.7
Present value of minimum payments		33.7	$ 29.5
Industrial Development Bond [Domain] | Letter of Credit [Member]
Debt Instrument [Line Items]
Letters of credit		11.7
Finance Lease, Liability, Payment, Due		$ 11.7