Allowance for Credit Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Credit loss expense (reversal) and available-for-sale, allowance for credit loss	$ 4.5	$ (27.0)	$ 6.5	$ (57.0)
Net recoveries (charge-offs)	(5.5)	(3.2)	$ (8.7)	(4.1)
Time period used for projecting future conditions to estimate credit losses			2 years
Financing receivable, excluding accrued interest, allowance for credit loss, period increase (decrease)	1.9		$ (0.2)
Provision for credit losses	6.0	(8.6)	9.4	(14.6)
Other financial assets, allowance for credit loss	$ 1.1	$ 1.2	$ 1.1	$ 1.2	$ 1.1	$ 1.0	$ 1.7	$ 0.8