Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) segment	Mar. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment	2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,142.9	$ 1,063.6
Foreign Exchange Trading Income	57.0	53.0
Other Noninterest Income (Loss)	(81.2)	96.8
Total Noninterest Income	1,118.7	1,213.4
Net Interest Income	528.1	531.2
Revenue	1,646.8	1,744.6
Provision for Credit Losses	(8.5)	15.0
Noninterest Expense	1,364.7	1,285.6
Income before Income Taxes	290.6	444.0
Provision for Income Taxes	75.9	109.4
Net Income	$ 214.7	$ 334.6
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 145,118.3	$ 148,059.9
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 (Loss)	0.0	0.0
Total Noninterest Income	0.0	0.0
Net Interest Income	(7.3)	(13.2)
Revenue	(7.3)	(13.2)
Provision for Credit Losses	0.0	0.0
Noninterest Expense	0.0	0.0
Income before Income Taxes	(7.3)	(13.2)
Provision for Income Taxes	(7.3)	(13.2)
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 (Loss)	(190.5)	(0.7)
Total Noninterest Income	(190.5)	(0.7)
Net Interest Income	0.0	0.0
Revenue	(190.5)	(0.7)
Provision for Credit Losses	(1.0)	0.0
Noninterest Expense	20.3	15.4
Income before Income Taxes	(209.8)	(16.1)
Provision for Income Taxes	(54.8)	(4.0)
Net Income	(155.0)	$ (12.1)
Percentage of Consolidated Net Income		(4.00%)
Average Assets	0.0	$ 0.0
ASSET SERVICING | Scenario, Adjustment
Noninterest Income
Net Interest Income	(31.0)
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	639.6	603.0
Foreign Exchange Trading Income	59.9	54.9
Other Noninterest Income (Loss)	70.8	63.2
Total Noninterest Income	770.3	721.1
Net Interest Income	293.8	312.1
Revenue	1,064.1	1,033.2
Provision for Credit Losses	(5.8)	(2.9)
Noninterest Expense	852.7	801.0
Income before Income Taxes	217.2	235.1
Provision for Income Taxes	56.6	60.5
Net Income	160.6	$ 174.6
Percentage of Consolidated Net Income		52.00%
Average Assets	106,955.0	$ 111,215.3
WEALTH MANAGEMENT | Scenario, Adjustment
Noninterest Income
Net Interest Income	31.0
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	503.3	460.6
Foreign Exchange Trading Income	(2.9)	(1.9)
Other Noninterest Income (Loss)	38.5	34.3
Total Noninterest Income	538.9	493.0
Net Interest Income	241.6	232.3
Revenue	780.5	725.3
Provision for Credit Losses	(1.7)	17.9
Noninterest Expense	491.7	469.2
Income before Income Taxes	290.5	238.2
Provision for Income Taxes	81.4	66.1
Net Income	209.1	$ 172.1
Percentage of Consolidated Net Income		52.00%
Average Assets	$ 38,163.3	$ 36,844.6