Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounts receivable credit loss allowance
Movement in Valuation Allowances and Reserves
Balance, Beginning of Year	$ 1.9	$ 0.5	$ 0.4
Charged to Costs and Expenses	0.1	1.4	0.1
Charged to Other Comprehensive Income		0.0	0.0
Charged to Retained Earnings		0.0	0.0
Write-offs		0.0	0.0
Balance, End of Year	2.0	1.9	0.5
Held-to-maturity debt securities credit loss allowance
Movement in Valuation Allowances and Reserves
Balance, Beginning of Year	0.9	0.0
Charged to Costs and Expenses	(0.4)	0.3
Charged to Other Comprehensive Income		0.0
Charged to Retained Earnings		0.6
Write-offs		0.0
Balance, End of Year	0.5	0.9	0.0
Deferred tax valuation allowance
Movement in Valuation Allowances and Reserves
Balance, Beginning of Year	8.4	13.0	15.5
Charged to Costs and Expenses	0.8	(1.9)	(1.9)
Charged to Other Comprehensive Income	(0.4)	(2.7)	(0.6)
Charged to Retained Earnings		0.0	0.0
Write-offs		0.0	0.0
Balance, End of Year	$ 8.8	$ 8.4	$ 13.0