Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,075.4	$ 961.5	$ 2,139.1	$ 1,965.1
Foreign Exchange Trading Income	70.6	71.3	149.3	160.2
Treasury Management Fees	11.3	11.4	22.5	22.4
Security Commissions and Trading Income	33.0	33.2	67.8	74.9
Other Operating Income	54.4	56.5	109.3	90.9
Investment Security Gains, net	0.0	0.1	0.0	0.1
Total Other Noninterest Income	169.3	172.5	348.9	348.5
Total Noninterest Income	1,244.7	1,134.0	2,488.0	2,313.6
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	479.2	397.7	948.9	815.3
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	521.2	485.4	1,037.6	995.9
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	19.5	27.4	37.8	50.9
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 55.5	$ 51.0	$ 114.8	$ 103.0