Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) segment	Mar. 31, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment	2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,063.6	$ 1,168.4
Foreign Exchange Trading Income	53.0	80.9
Other Noninterest Income	96.8	88.4
Total Noninterest Income	1,213.4	1,337.7
Net Interest Income	531.2	381.0
Revenue	1,744.6	1,718.7
Provision for Credit Losses	15.0	2.0
Noninterest Expense	1,285.6	1,205.9
Income before Income Taxes	444.0	510.8
Provision for Income Taxes	109.4	121.5
Net Income	$ 334.6	$ 389.3
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 148,059.9	$ 162,143.0
RECONCILING ITEMS
Noninterest Income
Trust, Investment and Other Servicing Fees	0.0	0.0
Foreign Exchange Trading Income	0.0	0.0
Other Noninterest Income	0.0	0.0
Total Noninterest Income	0.0	0.0
Net Interest Income	(13.2)	(6.7)
Revenue	(13.2)	(6.7)
Provision for Credit Losses	0.0	0.0
Noninterest Expense	0.0	0.0
Income before Income Taxes	(13.2)	(6.7)
Provision for Income Taxes	(13.2)	(6.7)
Net Income	0.0	0.0
OTHER
Noninterest Income
Trust, Investment and Other Servicing Fees	0.0	0.0
Foreign Exchange Trading Income	0.0	0.0
Other Noninterest Income	(0.7)	(4.5)
Total Noninterest Income	(0.7)	(4.5)
Net Interest Income	0.0	0.0
Revenue	(0.7)	(4.5)
Provision for Credit Losses	0.0	0.0
Noninterest Expense	15.4	2.9
Income before Income Taxes	(16.1)	(7.4)
Provision for Income Taxes	(4.0)	(1.9)
Net Income	$ (12.1)	$ (5.5)
Percentage of Consolidated Net Income	(4.00%)	(1.00%)
Average Assets	$ 0.0	$ 0.0
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	603.0	662.4
Foreign Exchange Trading Income	54.9	77.4
Other Noninterest Income	63.2	61.1
Total Noninterest Income	721.1	800.9
Net Interest Income	312.1	190.1
Revenue	1,033.2	991.0
Provision for Credit Losses	(2.9)	8.4
Noninterest Expense	801.0	757.9
Income before Income Taxes	235.1	224.7
Provision for Income Taxes	60.5	51.8
Net Income	$ 174.6	$ 172.9
Percentage of Consolidated Net Income	52.00%	44.00%
Average Assets	$ 111,215.3	$ 125,234.9
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	460.6	506.0
Foreign Exchange Trading Income	(1.9)	3.5
Other Noninterest Income	34.3	31.8
Total Noninterest Income	493.0	541.3
Net Interest Income	232.3	197.6
Revenue	725.3	738.9
Provision for Credit Losses	17.9	(6.4)
Noninterest Expense	469.2	445.1
Income before Income Taxes	238.2	300.2
Provision for Income Taxes	66.1	78.3
Net Income	$ 172.1	$ 221.9
Percentage of Consolidated Net Income	52.00%	57.00%
Average Assets	$ 36,844.6	$ 36,908.1