Allowance for Credit Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Receivables [Abstract]
Credit loss expense (reversal) and available-for-sale, allowance for credit loss	$ (27.0)	$ 66.0	$ (57.0)	$ 127.0
Net (charge-offs) recoveries	3.2	2.6	$ 4.1	1.9
Time period used for projecting future conditions to estimate credit losses			2 years
Other financial assets, allowance for credit loss	$ 1.2	$ 1.3	$ 1.2	$ 1.3	$ 1.7	$ 0.8	$ 1.1	$ 0.0