Allowance for Credit Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Receivables [Abstract]
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Allowance for credit loss	$ 165.4	$ 147.2	$ 104.5	$ 190.7
Stockholders equity	(11,457.9)	(10,879.7)	(11,091.0)	(11,688.3)
Credit loss expense (reversal) and available-for-sale, allowance for credit loss	(30.0)	61.0
Net (charge-offs) recoveries	$ 0.9	(0.7)
Time period used for projecting future conditions to estimate credit losses	2 years
Other financial assets, allowance for credit loss	$ 1.7	$ 1.1	$ 0.0	$ 0.8