Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Jun. 30, 2023 USD ($) segment	Jun. 30, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment					2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,096.3		$ 1,143.4		$ 2,159.9	$ 2,311.8
Foreign Exchange Trading Income	50.1		77.6		103.1	158.5
Other Noninterest Income	99.2		89.0		196.0	177.4
Total Noninterest Income	1,245.6		1,310.0		2,459.0	2,647.7
Net Interest Income	511.5		458.7		1,042.7	839.7
Revenue	1,757.1		1,768.7		3,501.7	3,487.4
(Release of) Provision for Credit Losses	(15.5)		4.5		(0.5)	6.5
Noninterest Expense	1,331.9		1,223.6		2,617.5	2,429.5
Income before Income Taxes	440.7		540.6		884.7	1,051.4
Provision for Income Taxes	108.9		144.4		218.3	265.9
Net Income	$ 331.8	$ 334.6	$ 396.2	$ 389.3	$ 666.4	$ 785.5
Percentage of Consolidated Net Income	100.00%		100.00%		100.00%	100.00%
Average Assets	$ 145,899.6		$ 154,084.1		$ 146,973.8	$ 158,091.3
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	0.0		0.0		0.0	0.0
Total Noninterest Income	0.0		0.0		0.0	0.0
Net Interest Income	(13.1)		(11.1)		(26.3)	(17.8)
Revenue	(13.1)		(11.1)		(26.3)	(17.8)
(Release of) 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	(13.1)		(11.1)		(26.3)	(17.8)
Provision for Income Taxes	(13.1)		(11.1)		(26.3)	(17.8)
Net Income	0.0		0.0		0.0	0.0
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	(10.9)		(5.6)		(11.6)	(10.1)
Total Noninterest Income	(10.9)		(5.6)		(11.6)	(10.1)
Net Interest Income	0.0		0.0		0.0	0.0
Revenue	(10.9)		(5.6)		(11.6)	(10.1)
(Release of) Provision for Credit Losses	0.0		0.0		0.0	0.0
Noninterest Expense	6.2		33.4		21.6	36.3
Income before Income Taxes	(17.1)		(39.0)		(33.2)	(46.4)
Provision for Income Taxes	(4.3)		(9.7)		(8.3)	(11.6)
Net Income	$ (12.8)		$ (29.3)		$ (24.9)	$ (34.8)
Percentage of Consolidated Net Income	(4.00%)		(7.00%)		(4.00%)	(4.00%)
Average Assets	$ 0.0		$ 0.0		$ 0.0	$ 0.0
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	621.2		642.8		1,224.2	1,305.2
Foreign Exchange Trading Income	52.0		74.8		106.9	152.2
Other Noninterest Income	69.7		61.8		132.9	122.9
Total Noninterest Income	742.9		779.4		1,464.0	1,580.3
Net Interest Income	309.3		255.1		621.4	445.2
Revenue	1,052.2		1,034.5		2,085.4	2,025.5
(Release of) Provision for Credit Losses	(3.5)		0.5		(6.4)	8.9
Noninterest Expense	849.4		751.1		1,650.4	1,509.0
Income before Income Taxes	206.3		282.9		441.4	507.6
Provision for Income Taxes	52.6		74.5		113.1	126.3
Net Income	$ 153.7		$ 208.4		$ 328.3	$ 381.3
Percentage of Consolidated Net Income	46.00%		53.00%		49.00%	49.00%
Average Assets	$ 111,029.9		$ 117,047.6		$ 111,143.6	$ 121,114.2
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	475.1		500.6		935.7	1,006.6
Foreign Exchange Trading Income	(1.9)		2.8		(3.8)	6.3
Other Noninterest Income	40.4		32.8		74.7	64.6
Total Noninterest Income	513.6		536.2		1,006.6	1,077.5
Net Interest Income	215.3		214.7		447.6	412.3
Revenue	728.9		750.9		1,454.2	1,489.8
(Release of) Provision for Credit Losses	(12.0)		4.0		5.9	(2.4)
Noninterest Expense	476.3		439.1		945.5	884.2
Income before Income Taxes	264.6		307.8		502.8	608.0
Provision for Income Taxes	73.7		90.7		139.8	169.0
Net Income	$ 190.9		$ 217.1		$ 363.0	$ 439.0
Percentage of Consolidated Net Income	58.00%		54.00%		55.00%	55.00%
Average Assets	$ 34,869.7		$ 37,036.5		$ 35,830.2	$ 36,977.1