Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 961.5	$ 955.5	$ 1,965.1	$ 1,884.4
Foreign Exchange Trading Income	71.3	60.5	160.2	126.7
Treasury Management Fees	11.4	11.2	22.4	22.9
Security Commissions and Trading Income	33.2	23.4	74.9	46.7
Other Operating Income	56.5	38.9	90.9	67.9
Investment Security Gains (Losses), net	0.1	(0.3)	0.1	(0.5)
Total Other Noninterest Income	172.5	133.7	348.5	263.7
Total Noninterest Income	1,134.0	1,089.2	2,313.6	2,148.1
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	397.7	407.4	815.3	804.9
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	485.4	478.1	995.9	937.3
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	27.4	22.0	50.9	44.8
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 51.0	$ 48.0	$ 103.0	$ 97.4