Reporting Segments (Results of Reporting Segments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	$ 1,003.6	$ 928.9
Foreign Exchange Trading Income	88.9	66.2
Other Noninterest Income	87.1	63.8
Total Noninterest Income	1,179.6	1,058.9
Net Interest Income	416.2	429.8
Revenue	1,595.8	1,488.7
Provision for Credit Losses	61.0	0.0
Noninterest Expense	1,065.6	1,028.7
Income before Income Taxes	469.2	460.0
Provision for Income Taxes	108.6	112.9
Net Income	$ 360.6	$ 347.1
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 124,170.5	$ 119,416.7
FTE adjustments	8.1	7.8
CORPORATE & INSTITUTIONAL SERVICES
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	574.4	535.2
Foreign Exchange Trading Income	85.1	59.7
Other Noninterest Income	41.8	43.4
Total Noninterest Income	701.3	638.3
Net Interest Income	211.3	234.8
Revenue	912.6	873.1
Provision for Credit Losses	25.7	(1.1)
Noninterest Expense	659.3	648.0
Income before Income Taxes	227.6	226.2
Provision for Income Taxes	49.9	53.6
Net Income	$ 177.7	$ 172.6
Percentage of Consolidated Net Income	49.00%	50.00%
Average Assets	$ 92,715.3	$ 90,351.7
WEALTH MANAGEMENT
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	429.2	393.7
Foreign Exchange Trading Income	3.8	6.5
Other Noninterest Income	42.4	25.5
Total Noninterest Income	475.4	425.7
Net Interest Income	204.9	195.0
Revenue	680.3	620.7
Provision for Credit Losses	35.3	1.1
Noninterest Expense	394.4	379.9
Income before Income Taxes	250.6	239.7
Provision for Income Taxes	60.9	60.8
Net Income	$ 189.7	$ 178.9
Percentage of Consolidated Net Income	53.00%	51.00%
Average Assets	$ 31,455.2	$ 29,065.0
TREASURY AND OTHER
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	0.0	0.0
Foreign Exchange Trading Income	0.0	0.0
Other Noninterest Income	2.9	(5.1)
Total Noninterest Income	2.9	(5.1)
Net Interest Income	0.0	0.0
Revenue	2.9	(5.1)
Provision for Credit Losses	0.0	0.0
Noninterest Expense	11.9	0.8
Income before Income Taxes	(9.0)	(5.9)
Provision for Income Taxes	(2.2)	(1.5)
Net Income	$ (6.8)	$ (4.4)
Percentage of Consolidated Net Income	(2.00%)	(1.00%)
Average Assets	$ 0.0	$ 0.0