Reporting Segments (Information by Reporting Segment) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,341.4	$ 1,213.8
Foreign Exchange Trading Income	87.7	58.7
Other Noninterest Income (Loss)	122.5	99.4
Total Noninterest Income	1,551.6	1,371.9
Net interest income	654.0	568.1
Revenue	2,205.6	1,940.0
Provision for Credit Losses	(3.0)	1.0
Compensation and Benefits	822.2	754.1
Outside Services	236.7	245.2
Allocated Expense	0.0	0.0
Other Segment Items	449.1	418.3
Total Noninterest Expense	1,508.0	1,417.6
Income before Income Taxes	700.6	521.4
Provision for Income Taxes	175.1	129.4
Net Income	$ 525.5	$ 392.0
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 165,297.3	$ 150,262.1
Average Loans	40,894.3	41,076.5
Average Deposits	129,031.8	115,919.1
FTE adjustments	7.6	5.6
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)	3.8	(2.7)
Total Noninterest Income	3.8	(2.7)
Net interest income	(7.2)	(5.7)
Revenue	(3.4)	(8.4)
Provision for Credit Losses	(2.3)	(0.2)
Compensation and Benefits	537.4	471.2
Outside Services	195.9	184.2
Allocated Expense	(1,138.9)	(1,018.9)
Other Segment Items	407.4	373.5
Total Noninterest Expense	1.8	10.0
Income before Income Taxes	(2.9)	(18.2)
Provision for Income Taxes	9.6	4.1
Net Income	$ (12.5)	$ (22.3)
Percentage of Consolidated Net Income	(2.00%)	(6.00%)
Average Assets	$ 141.0	$ 1,333.0
Average Loans	0.0	0.0
Average Deposits	141.0	1,333.0
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	740.5	671.9
Foreign Exchange Trading Income	90.9	63.9
Other Noninterest Income (Loss)	84.9	68.6
Total Noninterest Income	916.3	804.4
Net interest income	401.7	323.7
Revenue	1,318.0	1,128.1
Provision for Credit Losses	(2.3)	2.1
Compensation and Benefits	107.5	111.2
Outside Services	29.8	46.7
Allocated Expense	788.0	710.3
Other Segment Items	21.7	22.3
Total Noninterest Expense	947.0	890.5
Income before Income Taxes	373.3	235.5
Provision for Income Taxes	83.2	50.9
Net Income	$ 290.1	$ 184.6
Percentage of Consolidated Net Income	55.00%	47.00%
Average Assets	$ 125,539.4	$ 109,777.1
Average Loans	5,632.5	5,749.3
Average Deposits	102,421.0	89,296.5
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	600.9	541.9
Foreign Exchange Trading Income	(3.2)	(5.2)
Other Noninterest Income (Loss)	33.8	33.5
Total Noninterest Income	631.5	570.2
Net interest income	259.5	250.1
Revenue	891.0	820.3
Provision for Credit Losses	1.6	(0.9)
Compensation and Benefits	177.3	171.7
Outside Services	11.0	14.3
Allocated Expense	350.9	308.6
Other Segment Items	20.0	22.5
Total Noninterest Expense	559.2	517.1
Income before Income Taxes	330.2	304.1
Provision for Income Taxes	82.3	74.4
Net Income	$ 247.9	$ 229.7
Percentage of Consolidated Net Income	47.00%	59.00%
Average Assets	$ 39,616.9	$ 39,152.0
Average Loans	35,261.8	35,327.2
Average Deposits	$ 26,469.8	$ 25,289.6