Allowance for Credit Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Receivables [Abstract]
Credit loss expense (reversal) and available-for-sale, allowance for credit loss	$ (13.0)	$ 0.5	$ (70.0)	$ 127.5
Net (charge-offs) recoveries	1.1	0.4	$ 5.2	2.3
Time period used for projecting future conditions to estimate credit losses			2 years
Other financial assets, allowance for credit loss	$ 1.0	$ 0.7	$ 1.0	$ 0.7	$ 1.2	$ 0.8	$ 1.3	$ 0.0