Revenue from Contracts with Clients (Revenue Disaggregated by Major Source) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 3,995.0	$ 3,852.1	$ 3,753.7
Foreign Exchange Trading Income	290.4	250.9	307.2
Treasury Management Fees	45.4	44.5	51.8
Security Commissions and Trading Income	133.2	103.6	98.3
Other Operating Income	194.0	145.5	127.5
Investment Security Gains (Losses), net	(0.4)	(1.4)	(1.0)
Total Other Noninterest Income	662.6	543.1	583.8
Total Noninterest Income	4,657.6	4,395.2	4,337.5
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	1,674.3	1,636.4	1,589.1
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	2,029.3	1,930.6	1,862.6
Securities Lending
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	88.3	87.7	102.8
Other
Disaggregation of Revenue [Line Items]
Trust, Investment and Other Servicing Fees	$ 203.1	$ 197.4	$ 199.2