Summary of Significant Accounting Policies Lessee Accounting (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020		Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Renewal Term		5 years		5 years
Lessee, Operating Lease, Option to Terminate				one year
Finance Lease, Principal Payments				$ 0.0
Operating lease expense		$ 4.2	$ 3.7	12.1	$ 12.2
Short-term lease expense		0.0	$ 0.7	0.2	2.1
Right-of-use assets (1)	[1]	92.2		92.2			$ 77.1
Lease liabilities (2)	[2]	$ 116.2		$ 116.2			$ 96.9
Weighted average remaining lease term		10 years 6 months		10 years 6 months			11 years 3 months 18 days
Weighted average discount rate		3.00%		3.00%			3.30%
Cash flows from operating activities				$ 12.1	12.2
Right-of-use assets recognized in exchange for new lease liabilities (3)				26.6	$ 53.6	[3]
Remaining three months of 2021		$ 4.0		4.0
2022		19.3		19.3
2023		17.5		17.5
2024		12.9		12.9
2025		10.3		10.3
Thereafter		72.9		72.9
Lessee, Operating Lease, Liability, to be Paid, Total		136.9		136.9
Less: Present value adjustment		$ (20.7)		$ (20.7)
Minimum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract		1 year		1 year
Maximum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract		16 years		16 years
Railcar Leasing and Management Services Group [Member]
Lessee, Lease, Description [Line Items]
Remaining three months of 2021		$ 2.9		$ 2.9
2022		11.1		11.1
2023		9.3		9.3
2024		5.9		5.9
2025		4.0		4.0
Thereafter		8.1		8.1
Lessee, Operating Lease, Liability, to be Paid, Total		41.3		41.3
Consolidated Subsidiaries, Excluding Leasing [Member]
Lessee, Lease, Description [Line Items]
Remaining three months of 2021		1.1		1.1
2022		8.2		8.2
2023		8.2		8.2
2024		7.0		7.0
2025		6.3		6.3
Thereafter		64.8		64.8
Lessee, Operating Lease, Liability, to be Paid, Total		$ 95.6		$ 95.6

[1] Included in other assets in our Consolidated Balance Sheets.

[2] Included in other liabilities in our Consolidated Balance Sheets.

[3] Includes the commencement of the new headquarters facility for the nine months ended September 30, 2020