Reporting Segments (Information by Reporting Segment) (Detail) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,265.5			$ 1,196.6			$ 3,710.4	$ 3,505.6
Foreign Exchange Trading Income	57.2			54.1			166.5	169.5
Other Noninterest Income (Loss)	111.9			155.5			317.0	1,042.4
Total Noninterest Income	1,434.6			1,406.2			4,193.9	4,717.5
Net interest income	590.8			562.3			1,769.4	1,613.3
Revenue	2,025.4			1,968.5			5,963.3	6,330.8
Provision for Credit Losses	(17.0)			8.0			0.5	7.5
Compensation	625.3			583.6			1,884.5	1,875.9
Employee Benefits	115.2			109.2			342.6	310.5
Outside Services	248.2			256.3			740.4	746.5
Allocated Expense	0.0			0.0			0.0	0.0
Other Segment Items	434.2			410.3			1,289.6	1,325.1
Total Noninterest Expense	1,422.9			1,359.4			4,257.1	4,258.0
Income before Income Taxes	619.5			601.1			1,705.7	2,065.3
Provision for Income Taxes	161.9			136.2			434.8	489.6
Net Income	$ 457.6	$ 421.3	$ 392.0	$ 464.9	$ 896.1	$ 214.7	$ 1,270.9	$ 1,575.7
Percentage of Consolidated Net Income	100.00%			100.00%			100.00%	100.00%
Average Assets	$ 151,041.5			$ 146,842.9			$ 153,010.4	$ 146,654.8
Average Loans	41,500.6			39,884.0			41,246.6	40,831.6
Average Deposits	116,700.6			112,560.7			118,335.4	112,754.2
FTE adjustments	5.5			7.1			15.8	21.3
Other
Noninterest Income
Trust, Investment and Other Servicing Fees	0.0			0.0			0.0	0.0
Foreign Exchange Trading Income	0.0			0.0			0.0	0.0
Other Noninterest Income (Loss)	(4.0)			53.3			(6.2)	741.6
Total Noninterest Income	(4.0)			53.3			(6.2)	741.6
Net interest income	(6.3)			(7.4)			(17.0)	(17.3)
Revenue	(10.3)			45.9			(23.2)	724.3
Provision for Credit Losses	1.4			(3.8)			2.6	(6.3)
Compensation	403.2			354.6			1,201.0	1,118.9
Employee Benefits	75.9			67.5			224.7	193.5
Outside Services	210.2			201.1			580.9	566.8
Allocated Expense	(1,078.9)			(979.8)			(3,143.4)	(2,938.7)
Other Segment Items	394.9			370.7			1,162.2	1,200.2
Total Noninterest Expense	5.3			14.1			25.4	140.7
Income before Income Taxes	(17.0)			35.6			(51.2)	589.9
Provision for Income Taxes	13.9			2.7			27.8	138.4
Net Income	$ (30.9)			$ 32.9			$ (79.0)	$ 451.5
Percentage of Consolidated Net Income	(7.00%)			7.00%			(6.00%)	29.00%
Average Assets	$ 1,134.9			$ 745.7			$ 1,348.6	$ 578.6
Average Loans	0.0			0.0			0.0	0.0
Average Deposits	1,134.9			745.7			1,348.6	578.6
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	706.9			667.1			2,070.6	1,957.3
Foreign Exchange Trading Income	65.5			59.5			190.4	181.6
Other Noninterest Income (Loss)	77.0			66.7			216.2	196.8
Total Noninterest Income	849.4			793.3			2,477.2	2,335.7
Net interest income	339.9			320.9			1,010.8	896.2
Revenue	1,189.3			1,114.2			3,488.0	3,231.9
Provision for Credit Losses	(6.1)			(0.6)			(0.1)	(1.9)
Compensation	78.8			90.3			249.1	318.4
Employee Benefits	16.8			18.2			50.8	52.3
Outside Services	24.0			43.6			114.2	145.6
Allocated Expense	763.6			682.7			2,213.5	2,037.7
Other Segment Items	18.1			21.6			59.9	66.5
Total Noninterest Expense	901.3			856.4			2,687.5	2,620.5
Income before Income Taxes	294.1			258.4			800.6	613.3
Provision for Income Taxes	64.3			56.7			173.2	134.5
Net Income	$ 229.8			$ 201.7			$ 627.4	$ 478.8
Percentage of Consolidated Net Income	50.00%			43.00%			49.00%	30.00%
Average Assets	$ 110,056.4			$ 107,362.3			$ 112,297.8	$ 107,447.0
Average Loans	5,399.9			5,615.8			5,652.7	6,329.8
Average Deposits	90,195.3			86,635.7			91,669.5	86,516.2
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	558.6			529.5			1,639.8	1,548.3
Foreign Exchange Trading Income	(8.3)			(5.4)			(23.9)	(12.1)
Other Noninterest Income (Loss)	38.9			35.5			107.0	104.0
Total Noninterest Income	589.2			559.6			1,722.9	1,640.2
Net interest income	257.2			248.8			775.6	734.4
Revenue	846.4			808.4			2,498.5	2,374.6
Provision for Credit Losses	(12.3)			12.4			(2.0)	15.7
Compensation	143.3			138.7			434.4	438.6
Employee Benefits	22.5			23.5			67.1	64.7
Outside Services	14.0			11.6			45.3	34.1
Allocated Expense	315.3			297.1			929.9	901.0
Other Segment Items	21.2			18.0			67.5	58.4
Total Noninterest Expense	516.3			488.9			1,544.2	1,496.8
Income before Income Taxes	342.4			307.1			956.3	862.1
Provision for Income Taxes	83.7			76.8			233.8	216.7
Net Income	$ 258.7			$ 230.3			$ 722.5	$ 645.4
Percentage of Consolidated Net Income	57.00%			50.00%			57.00%	41.00%
Average Assets	$ 39,850.2			$ 38,734.9			$ 39,364.0	$ 38,629.2
Average Loans	36,100.7			34,268.2			35,593.9	34,501.8
Average Deposits	$ 25,370.4			$ 25,179.3			$ 25,317.3	$ 25,659.4