Reporting Segments (Information by Reporting Segment) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,213.8	$ 1,142.9
Foreign Exchange Trading Income	58.7	57.0
Other Noninterest Income (Loss)	99.4	(81.2)
Total Noninterest Income	1,371.9	1,118.7
Net interest income	568.1	528.1
Revenue	1,940.0	1,646.8
Provision for Credit Losses	1.0	(8.5)
Compensation	644.4	627.1
Employee Benefits	109.7	101.1
Outside Services	245.2	229.3
Allocated Expense	0.0	0.0
Other Segment Items	418.3	407.2
Total Noninterest Expense	1,417.6	1,364.7
Income before Income Taxes	521.4	290.6
Provision for Income Taxes	129.4	75.9
Net Income	$ 392.0	$ 214.7
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 150,262.1	$ 145,118.3
Average Loans	41,076.5	41,586.9
Average Deposits	115,919.1	112,362.6
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)	(2.7)	(190.4)
Total Noninterest Income	(2.7)	(190.4)
Net interest income	(5.3)	(5.7)
Revenue	(8.0)	(196.1)
Provision for Credit Losses	(0.2)	(1.0)
Compensation	398.5	386.5
Employee Benefits	70.1	63.4
Outside Services	172.1	158.1
Allocated Expense	(1,003.7)	(949.8)
Other Segment Items	373.0	367.6
Total Noninterest Expense	10.0	25.8
Income before Income Taxes	(17.8)	(220.9)
Provision for Income Taxes	4.2	(46.1)
Net Income	$ (22.0)	(174.8)
Percentage of Consolidated Net Income	(6.00%)
Average Assets	$ 1,333.0	106.0
Average Loans	0.0	0.0
Average Deposits	1,333.0	106.0
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	671.9	639.6
Foreign Exchange Trading Income	63.9	59.9
Other Noninterest Income (Loss)	68.6	70.7
Total Noninterest Income	804.4	770.2
Net interest income	323.2	292.4
Revenue	1,127.6	1,062.6
Provision for Credit Losses	2.1	(5.8)
Compensation	94.5	95.6
Employee Benefits	17.4	17.0
Outside Services	58.7	61.1
Allocated Expense	697.2	654.2
Other Segment Items	22.7	21.3
Total Noninterest Expense	890.5	849.2
Income before Income Taxes	235.0	219.2
Provision for Income Taxes	50.8	48.4
Net Income	$ 184.2	170.8
Percentage of Consolidated Net Income	47.00%
Average Assets	$ 109,776.8	106,849.0
Average Loans	5,749.3	6,909.5
Average Deposits	89,296.5	86,688.6
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	541.9	503.3
Foreign Exchange Trading Income	(5.2)	(2.9)
Other Noninterest Income (Loss)	33.5	38.5
Total Noninterest Income	570.2	538.9
Net interest income	250.2	241.4
Revenue	820.4	780.3
Provision for Credit Losses	(0.9)	(1.7)
Compensation	151.4	145.0
Employee Benefits	22.2	20.7
Outside Services	14.4	10.1
Allocated Expense	306.5	295.6
Other Segment Items	22.6	18.3
Total Noninterest Expense	517.1	489.7
Income before Income Taxes	304.2	292.3
Provision for Income Taxes	74.4	73.6
Net Income	$ 229.8	218.7
Percentage of Consolidated Net Income	59.00%
Average Assets	$ 39,152.3	38,163.3
Average Loans	35,327.2	34,677.4
Average Deposits	$ 25,289.6	$ 25,568.0