Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,003.8	$ 975.5	$ 2,968.9	$ 2,859.9
Foreign Exchange Trading Income	61.6	59.7	221.8	186.4
Treasury Management Fees	11.6	11.2	34.0	34.1
Security Commissions and Trading Income	26.0	29.1	100.9	75.8
Other Operating Income	53.5	45.1	144.4	113.0
Investment Security Gains (Losses), net	0.0	(0.4)	0.1	(0.9)
Total Other Noninterest Income	152.7	144.7	501.2	408.4
Total Noninterest Income	1,156.5	1,120.2	3,470.1	3,268.3
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	416.4	414.8	1,231.7	1,219.7
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	519.3	491.4	1,515.2	1,428.7
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	19.8	20.1	70.7	64.9
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 48.3	$ 49.2	$ 151.3	$ 146.6