Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2024 USD ($) segment	Jun. 30, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment					2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,166.1		$ 1,096.3		$ 2,309.0	$ 2,159.9
Foreign Exchange Trading Income	58.4		50.1		115.4	103.1
Other Noninterest Income (Loss)	968.1		99.2		886.9	196.0
Total Noninterest Income	2,192.6		1,245.6		3,311.3	2,459.0
Net Interest Income	522.9		511.5		1,051.0	1,042.7
Revenue	2,715.5		1,757.1		4,362.3	3,501.7
Provision for Credit Losses	8.0		(15.5)		(0.5)	(0.5)
Noninterest Expense	1,533.9		1,331.9		2,898.6	2,617.5
Income before Income Taxes	1,173.6		440.7		1,464.2	884.7
Provision for Income Taxes	277.5		108.9		353.4	218.3
Net Income	$ 896.1	$ 214.7	$ 331.8	$ 334.6	$ 1,110.8	$ 666.4
Percentage of Consolidated Net Income	100.00%		100.00%		100.00%	100.00%
Average Assets	$ 148,001.2		$ 145,899.6		$ 146,559.8	$ 146,973.8
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)	875.9		(10.9)		685.4	(11.6)
Total Noninterest Income	875.9		(10.9)		685.4	(11.6)
Net Interest Income	0.0		0.0		0.0	0.0
Revenue	875.9		(10.9)		685.4	(11.6)
Provision for Credit Losses	(1.5)		0.0		(2.5)	0.0
Noninterest Expense	91.4		6.2		111.7	21.6
Income before Income Taxes	786.0		(17.1)		576.2	(33.2)
Provision for Income Taxes	185.5		(4.3)		130.7	(8.3)
Net Income	$ 600.5		$ (12.8)		$ 445.5	$ (24.9)
Percentage of Consolidated Net Income	67.00%		(4.00%)		40.00%	(4.00%)
Average Assets	$ 0.0		$ 0.0		$ 0.0	$ 0.0
RECONCILING ITEMS
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)	0.0		0.0		0.0	0.0
Total Noninterest Income	0.0		0.0		0.0	0.0
Net Interest Income	(6.9)		(13.1)		(14.2)	(26.3)
Revenue	(6.9)		(13.1)		(14.2)	(26.3)
Provision for Credit Losses	0.0		0.0		0.0	0.0
Noninterest Expense	0.0		0.0		0.0	0.0
Income before Income Taxes	(6.9)		(13.1)		(14.2)	(26.3)
Provision for Income Taxes	(6.9)		(13.1)		(14.2)	(26.3)
Net Income	0.0		0.0		0.0	0.0
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	650.6		621.2		1,290.2	1,224.2
Foreign Exchange Trading Income	62.2		52.0		122.1	106.9
Other Noninterest Income (Loss)	61.1		69.7		131.9	132.9
Total Noninterest Income	773.9		742.9		1,544.2	1,464.0
Net Interest Income	285.3		309.3		579.1	621.4
Revenue	1,059.2		1,052.2		2,123.3	2,085.4
Provision for Credit Losses	4.5		(3.5)		(1.3)	(6.4)
Noninterest Expense	920.6		849.4		1,773.3	1,650.4
Income before Income Taxes	134.1		206.3		351.3	441.4
Provision for Income Taxes	32.4		52.6		89.0	113.1
Net Income	$ 101.7		$ 153.7		$ 262.3	$ 328.3
Percentage of Consolidated Net Income	11.00%		46.00%		24.00%	49.00%
Average Assets	$ 108,728.3		$ 111,029.9		$ 107,850.4	$ 111,143.6
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	515.5		475.1		1,018.8	935.7
Foreign Exchange Trading Income	(3.8)		(1.9)		(6.7)	(3.8)
Other Noninterest Income (Loss)	31.1		40.4		69.6	74.7
Total Noninterest Income	542.8		513.6		1,081.7	1,006.6
Net Interest Income	244.5		215.3		486.1	447.6
Revenue	787.3		728.9		1,567.8	1,454.2
Provision for Credit Losses	5.0		(12.0)		3.3	5.9
Noninterest Expense	521.9		476.3		1,013.6	945.5
Income before Income Taxes	260.4		264.6		550.9	502.8
Provision for Income Taxes	66.5		73.7		147.9	139.8
Net Income	$ 193.9		$ 190.9		$ 403.0	$ 363.0
Percentage of Consolidated Net Income	22.00%		58.00%		36.00%	55.00%
Average Assets	$ 39,272.9		$ 34,869.7		$ 38,709.4	$ 35,830.2