Reporting Segments and Related Information - Information by Reporting Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 5,017.8	$ 4,727.8	$ 4,361.8
Foreign Exchange Trading Income	240.8	231.2	203.9
Other Noninterest Income (Loss)	416.8	1,154.3	225.8
Total Noninterest Income	5,675.4	6,113.3	4,791.5
Net interest income	2,411.0	2,177.1	1,982.0
Revenue	8,086.4	8,290.4	6,773.5
Provision for Credit Losses	(7.5)	(3.0)	24.5
Compensation	2,571.3	2,471.1	2,321.8
Employee Benefits	462.1	417.8	405.2
Outside Services	988.5	998.0	906.5
Allocated Expense	0.0	0.0	0.0
Other Segment Items	1,732.5	1,747.0	1,650.7
Total Noninterest Expense	5,754.4	5,633.9	5,284.2
Income before Income Taxes	2,339.5	2,659.5	1,464.8
Provision for Income Taxes	602.6	628.4	357.5
NET INCOME	$ 1,736.9	$ 2,031.1	$ 1,107.3
Percentage of Consolidated Net Income	100.00%	100.00%	100.00%
Average Assets	$ 153,493.2	$ 146,633.5	$ 142,649.2
Average Loans	41,073.1	40,916.7	42,177.0
Average Deposits	118,711.9	112,700.3	105,245.5
Severance costs	58.8	85.2
Software amortization acceleration and dispositions		16.4
Defined benefit plan, loss on securities due to repositioning		(6.5)
Segment reporting information, fully taxable-equivalent adjustment	28.5	31.8	57.5
Unrealized gain on Visa Class B swap agreements	19.2
FDIC Insurance Premiums	(17.8)	(43.0)	(112.0)
Gain on Visa Exchange Offer		878.4
Gain on sale of equity investment		68.1
Investment security loss	0.0	189.3	169.5
FDIC Special Assessment
Noninterest Income
FDIC Insurance Premiums		(14.7)	(84.6)
Other
Noninterest Income
Trust, Investment and Other Servicing Fees	0.0	0.0	0.0
Foreign Exchange Trading Income	0.0	0.0	0.0
Other Noninterest Income (Loss)	(25.2)	743.0	(188.4)
Total Noninterest Income	(25.2)	743.0	(188.4)
Net interest income	(29.8)	(25.8)	(57.5)
Revenue	(55.0)	717.2	(245.9)
Provision for Credit Losses	3.2	(7.2)	0.0
Compensation	1,665.4	1,495.3	1,409.5
Employee Benefits	304.3	260.4	256.0
Outside Services	805.0	763.4	672.0
Allocated Expense	(4,309.5)	(3,939.4)	(3,674.7)
Other Segment Items	1,562.1	1,575.7	1,465.9
Total Noninterest Expense	27.3	155.4	128.7
Income before Income Taxes	(85.5)	569.0	(374.6)
Provision for Income Taxes	40.9	131.1	(75.5)
NET INCOME	$ (126.4)	$ 437.9	$ (299.1)
Percentage of Consolidated Net Income	(7.00%)	21.00%	(27.00%)
Average Assets	$ 1,171.5	$ 450.8	$ 70.5
Average Loans	0.0	0.0	0.0
Average Deposits	1,171.5	450.8	70.5
Asset Servicing segment | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	2,800.2	2,632.8	2,461.9
Foreign Exchange Trading Income	268.0	247.2	213.0
Other Noninterest Income (Loss)	298.2	271.0	263.4
Total Noninterest Income	3,366.4	3,151.0	2,938.3
Net interest income	1,398.3	1,209.5	1,197.3
Revenue	4,764.7	4,360.5	4,135.6
Provision for Credit Losses	(3.2)	(4.6)	0.5
Compensation	328.5	399.3	361.1
Employee Benefits	66.9	70.0	66.2
Outside Services	122.1	188.2	191.3
Allocated Expense	3,047.5	2,738.6	2,542.1
Other Segment Items	75.8	91.6	110.0
Total Noninterest Expense	3,640.8	3,487.7	3,270.7
Income before Income Taxes	1,127.1	877.4	864.4
Provision for Income Taxes	244.5	192.4	187.1
NET INCOME	$ 882.6	$ 685.0	$ 677.3
Percentage of Consolidated Net Income	51.00%	34.00%	61.00%
Average Assets	$ 113,080.3	$ 107,700.1	$ 101,402.1
Average Loans	5,676.2	6,315.5	7,372.6
Average Deposits	91,906.8	86,691.3	81,742.1
Wealth Management segment | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	2,217.6	2,095.0	1,899.9
Foreign Exchange Trading Income	(27.2)	(16.0)	(9.1)
Other Noninterest Income (Loss)	143.8	140.3	150.8
Total Noninterest Income	2,334.2	2,219.3	2,041.6
Net interest income	1,042.5	993.4	842.2
Revenue	3,376.7	3,212.7	2,883.8
Provision for Credit Losses	(7.5)	8.8	24.0
Compensation	577.4	576.5	551.2
Employee Benefits	90.9	87.4	83.0
Outside Services	61.4	46.4	43.2
Allocated Expense	1,262.0	1,200.8	1,132.6
Other Segment Items	94.6	79.7	74.8
Total Noninterest Expense	2,086.3	1,990.8	1,884.8
Income before Income Taxes	1,297.9	1,213.1	975.0
Provision for Income Taxes	317.2	304.9	245.9
NET INCOME	$ 980.7	$ 908.2	$ 729.1
Percentage of Consolidated Net Income	56.00%	45.00%	66.00%
Average Assets	$ 39,241.4	$ 38,482.6	$ 41,176.6
Average Loans	35,396.9	34,601.2	34,804.4
Average Deposits	$ 25,633.6	$ 25,558.2	$ 23,432.9