Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment	2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,063.7	$ 1,003.6
Foreign Exchange Trading Income	78.7	88.9
Other Noninterest Income	100.9	87.1
Total Noninterest Income	1,243.3	1,179.6
Net Interest Income	346.7	416.2
Revenue	1,590.0	1,595.8
Provision for Credit Losses	(30.0)	61.0
Noninterest Expense	1,117.5	1,065.6
Income before Income Taxes	502.5	469.2
Provision for Income Taxes	127.4	108.6
Net Income	$ 375.1	$ 360.6
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 153,255.8	$ 124,170.5
FTE adjustments	6.6	8.1
CORPORATE & INSTITUTIONAL SERVICES
Noninterest Income
Trust, Investment and Other Servicing Fees	620.5	574.4
Foreign Exchange Trading Income	74.5	85.1
Other Noninterest Income	60.3	41.8
Total Noninterest Income	755.3	701.3
Net Interest Income	160.7	211.3
Revenue	916.0	912.6
Provision for Credit Losses	(5.4)	25.7
Noninterest Expense	713.1	659.3
Income before Income Taxes	208.3	227.6
Provision for Income Taxes	50.1	49.9
Net Income	$ 158.2	$ 177.7
Percentage of Consolidated Net Income	42.00%	49.00%
Average Assets	$ 120,157.7	$ 92,715.3
WEALTH MANAGEMENT
Noninterest Income
Trust, Investment and Other Servicing Fees	443.2	429.2
Foreign Exchange Trading Income	4.2	3.8
Other Noninterest Income	44.2	42.4
Total Noninterest Income	491.6	475.4
Net Interest Income	186.0	204.9
Revenue	677.6	680.3
Provision for Credit Losses	(24.6)	35.3
Noninterest Expense	403.1	394.4
Income before Income Taxes	299.1	250.6
Provision for Income Taxes	78.5	60.9
Net Income	$ 220.6	$ 189.7
Percentage of Consolidated Net Income	59.00%	53.00%
Average Assets	$ 33,098.1	$ 31,455.2
OTHER
Noninterest Income
Trust, Investment and Other Servicing Fees	0.0	0.0
Foreign Exchange Trading Income	0.0	0.0
Other Noninterest Income	(3.6)	2.9
Total Noninterest Income	(3.6)	2.9
Net Interest Income	0.0	0.0
Revenue	(3.6)	2.9
Provision for Credit Losses	0.0	0.0
Noninterest Expense	1.3	11.9
Income before Income Taxes	(4.9)	(9.0)
Provision for Income Taxes	(1.2)	(2.2)
Net Income	$ (3.7)	$ (6.8)
Percentage of Consolidated Net Income	(1.00%)	(2.00%)
Average Assets	$ 0.0	$ 0.0