Reporting Segments (Information by Reporting Segment) (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,349.5		$ 1,231.1		$ 2,690.9	$ 2,444.9
Foreign Exchange Trading Income	97.1		50.6		184.8	109.3
Other Noninterest Income (Loss)	575.9		105.7		698.5	205.1
Total Noninterest Income	2,022.5		1,387.4		3,574.2	2,759.3
Net interest income	675.5		610.5		1,329.5	1,178.6
Revenue	2,698.0		1,997.9		4,903.7	3,937.9
Provision for Credit Losses	(5.3)		16.5		(8.3)	17.5
Compensation and Benefits	868.0		732.5		1,690.2	1,486.6
Outside Services	246.3		247.0		483.0	492.2
Allocated Expense	0.0		0.0		0.0	0.0
Other Segment Items	524.3		437.1		973.4	855.4
Total Noninterest Expense	1,638.6		1,416.6		3,146.6	2,834.2
Income before Income Taxes	1,064.7		564.8		1,765.4	1,086.2
Provision for Income Taxes	272.5		143.5		447.6	272.9
Net Income	$ 792.2	$ 525.5	$ 421.3	$ 392.0	$ 1,317.8	$ 813.3
Percentage of Consolidated Net Income	100.00%		100.00%		100.00%	100.00%
Average Assets	$ 163,575.8		$ 157,719.2		$ 164,431.8	$ 154,011.3
Average Loans	41,567.6		41,158.0		41,232.8	41,117.4
Average Deposits	127,845.7		122,377.8		128,435.4	119,166.3
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)	450.8		0.5		454.6	(2.2)
Total Noninterest Income	450.8		0.5		454.6	(2.2)
Net interest income	(5.9)		(5.0)		(13.1)	(10.7)
Revenue	444.9		(4.5)		441.5	(12.9)
Provision for Credit Losses	(1.0)		1.4		(3.3)	1.2
Compensation and Benefits	580.0		478.0		1,117.4	949.2
Outside Services	201.3		186.5		397.2	370.7
Allocated Expense	(1,223.9)		(1,048.2)		(2,362.8)	(2,067.1)
Other Segment Items	480.6		394.0		888.0	767.5
Total Noninterest Expense	38.0		10.3		39.8	20.3
Income before Income Taxes	407.9		(16.2)		405.0	(34.4)
Provision for Income Taxes	116.4		9.7		125.9	13.8
Net Income	$ 291.5		$ (25.9)		$ 279.1	$ (48.2)
Percentage of Consolidated Net Income	36.00%		(7.00%)		21.00%	(6.00%)
Average Assets	$ 150.0		$ 1,580.1		$ 145.5	$ 1,457.2
Average Loans	0.0		0.0		0.0	0.0
Average Deposits	150.0		1,580.1		145.5	1,457.2
FTE adjustments	7.6		4.7		15.2	10.3
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	757.4		691.8		1,497.9	1,363.7
Foreign Exchange Trading Income	98.9		61.0		189.9	124.9
Other Noninterest Income (Loss)	89.3		70.6		174.2	139.2
Total Noninterest Income	945.6		823.4		1,862.0	1,627.8
Net interest income	416.1		347.2		817.8	670.9
Revenue	1,361.7		1,170.6		2,679.8	2,298.7
Provision for Credit Losses	(2.7)		3.9		(5.0)	6.0
Compensation and Benefits	111.7		90.9		219.2	202.1
Outside Services	31.4		43.5		61.2	90.2
Allocated Expense	875.3		741.5		1,663.4	1,451.8
Other Segment Items	22.7		19.4		44.4	41.7
Total Noninterest Expense	1,041.1		895.3		1,988.2	1,785.8
Income before Income Taxes	323.3		271.4		696.6	506.9
Provision for Income Taxes	72.9		58.2		156.1	109.1
Net Income	$ 250.4		$ 213.2		$ 540.5	$ 397.8
Percentage of Consolidated Net Income	32.00%		51.00%		41.00%	49.00%
Average Assets	$ 123,994.6		$ 117,044.6		$ 124,800.1	$ 113,432.9
Average Loans	5,800.6		5,812.8		5,717.0	5,781.2
Average Deposits	100,980.6		95,506.7		101,696.8	92,418.8
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	592.1		539.3		1,193.0	1,081.2
Foreign Exchange Trading Income	(1.8)		(10.4)		(5.1)	(15.6)
Other Noninterest Income (Loss)	35.8		34.6		69.7	68.1
Total Noninterest Income	626.1		563.5		1,257.6	1,133.7
Net interest income	265.3		268.3		524.8	518.4
Revenue	891.4		831.8		1,782.4	1,652.1
Provision for Credit Losses	(1.6)		11.2		0.0	10.3
Compensation and Benefits	176.3		163.6		353.6	335.3
Outside Services	13.6		17.0		24.6	31.3
Allocated Expense	348.6		306.7		699.4	615.3
Other Segment Items	21.0		23.7		41.0	46.2
Total Noninterest Expense	559.5		511.0		1,118.6	1,028.1
Income before Income Taxes	333.5		309.6		663.8	613.7
Provision for Income Taxes	83.2		75.6		165.6	150.0
Net Income	$ 250.3		$ 234.0		$ 498.2	$ 463.7
Percentage of Consolidated Net Income	32.00%		56.00%		38.00%	57.00%
Average Assets	$ 39,431.2		$ 39,094.5		$ 39,486.2	$ 39,121.2
Average Loans	35,767.0		35,345.2		35,515.8	35,336.2
Average Deposits	$ 26,715.1		$ 25,291.0		$ 26,593.1	$ 25,290.3