Investments - Components of Finance Lease Receivables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance lease receivables sold	$ 5.0	$ 2.7	$ 11.1
Finance Leases Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross minimum lease receivable	44.0	41.8
Allowance for credit losses	(0.2)	(0.3)
Estimated unguaranteed residual values	0.2	0.2
Capital Leases Net Investment In Sales Type Leases Minimum Payments To Be Received And Unguaranteed Residual Values	44.0	41.7
Unearned interest income	(1.5)	(2.8)
Unearned residuals	0.0	0.0
Capital Leases Net Investment In Sales Type Leases Unearned Interest Income And Residuals	1.5	2.8
Total	$ 42.5	$ 38.9