Revenue from Contracts with Customers (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Foreign Exchange Trading Income	$ 78.5	$ 48.1
Treasury Management Fees	14.0	14.7
Security Commissions and Trading Income	27.2	20.5
Other Operating Income	34.8	39.7
Investment Security Losses, net	(0.2)	(0.3)
Total Other Noninterest Income	154.3
Noninterest Income	1,092.0	930.9
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	395.9
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	465.6
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	26.2
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	50.0
Total Trust, Investment and Other Servicing Fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	937.7	$ 808.2
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	24.0
Other Operating Income
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 11.3