Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Jun. 30, 2022 USD ($) segment	Jun. 30, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment					2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,143.4		$ 1,075.4		$ 2,311.8	$ 2,139.1
Foreign Exchange Trading Income	77.6		70.6		158.5	149.3
Other Noninterest Income	89.0		98.7		177.4	199.6
Total Noninterest Income	1,310.0		1,244.7		2,647.7	2,488.0
Net Interest Income	458.7		335.6		839.7	675.7
Revenue	1,768.7		1,580.3		3,487.4	3,163.7
Provision for Credit Losses	4.5		(27.0)		6.5	(57.0)
Noninterest Expense	1,223.6		1,120.8		2,429.5	2,238.3
Income before Income Taxes	540.6		486.5		1,051.4	982.4
Provision for Income Taxes	144.4		118.4		265.9	239.2
Net Income	$ 396.2	$ 389.3	$ 368.1	$ 375.1	$ 785.5	$ 743.2
Percentage of Consolidated Net Income	100.00%		100.00%		100.00%	100.00%
Average Assets	$ 154,084.1		$ 154,300.1		$ 158,091.3	$ 153,780.8
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	(11.1)		(8.3)		(17.8)	(14.9)
Revenue	(11.1)		(8.3)		(17.8)	(14.9)
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	(11.1)		(8.3)		(17.8)	(14.9)
Provision for Income Taxes	(11.1)		(8.3)		(17.8)	(14.9)
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	(5.6)		(8.5)		(10.1)	(12.1)
Total Noninterest Income	(5.6)		(8.5)		(10.1)	(12.1)
Net Interest Income	0.0		0.0		0.0	0.0
Revenue	(5.6)		(8.5)		(10.1)	(12.1)
Provision for Credit Losses	0.0		0.0		0.0	0.0
Noninterest Expense	33.4		18.7		36.3	20.0
Income before Income Taxes	(39.0)		(27.2)		(46.4)	(32.1)
Provision for Income Taxes	(9.7)		(6.8)		(11.6)	(8.0)
Net Income	$ (29.3)		$ (20.4)		$ (34.8)	$ (24.1)
Percentage of Consolidated Net Income	(7.00%)		(6.00%)		(4.00%)	(3.00%)
Average Assets	$ 0.0		$ 0.0		$ 0.0	$ 0.0
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	642.8		611.5		1,305.2	1,232.0
Foreign Exchange Trading Income	74.8		67.9		152.2	142.4
Other Noninterest Income	61.8		68.9		122.9	129.2
Total Noninterest Income	779.4		748.3		1,580.3	1,503.6
Net Interest Income	255.1		153.1		445.2	313.8
Revenue	1,034.5		901.4		2,025.5	1,817.4
Provision for Credit Losses	0.5		(16.8)		8.9	(22.2)
Noninterest Expense	751.1		703.6		1,509.0	1,416.7
Income before Income Taxes	282.9		214.6		507.6	422.9
Provision for Income Taxes	74.5		53.0		126.3	103.1
Net Income	$ 208.4		$ 161.6		$ 381.3	$ 319.8
Percentage of Consolidated Net Income	53.00%		44.00%		49.00%	43.00%
Average Assets	$ 117,047.6		$ 119,502.3		$ 121,114.2	$ 119,820.7
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	500.6		463.9		1,006.6	907.1
Foreign Exchange Trading Income	2.8		2.7		6.3	6.9
Other Noninterest Income	32.8		38.3		64.6	82.5
Total Noninterest Income	536.2		504.9		1,077.5	996.5
Net Interest Income	214.7		190.8		412.3	376.8
Revenue	750.9		695.7		1,489.8	1,373.3
Provision for Credit Losses	4.0		(10.2)		(2.4)	(34.8)
Noninterest Expense	439.1		398.5		884.2	801.6
Income before Income Taxes	307.8		307.4		608.0	606.5
Provision for Income Taxes	90.7		80.5		169.0	159.0
Net Income	$ 217.1		$ 226.9		$ 439.0	$ 447.5
Percentage of Consolidated Net Income	54.00%		62.00%		55.00%	60.00%
Average Assets	$ 37,036.5		$ 34,797.8		$ 36,977.1	$ 33,960.1