Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment					2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 961.5		$ 955.5		$ 1,965.1	$ 1,884.4
Foreign Exchange Trading Income	71.3		60.5		160.2	126.7
Other Noninterest Income	101.2		73.2		188.3	137.0
Total Noninterest Income	1,134.0		1,089.2		2,313.6	2,148.1
Net Interest Income	379.8		425.1		796.0	854.9
Revenue	1,513.8		1,514.3		3,109.6	3,003.0
Provision for Credit Losses	66.0		(6.5)		127.0	(6.5)
Noninterest Expense	1,036.9		1,006.2		2,102.5	2,034.9
Income before Income Taxes	410.9		514.6		880.1	974.6
Provision for Income Taxes	97.6		125.2		206.2	238.1
Net Income	$ 313.3	$ 360.6	$ 389.4	$ 347.1	$ 673.9	$ 736.5
Percentage of Consolidated Net Income	100.00%		100.00%		100.00%	100.00%
Average Assets	$ 138,770.6		$ 116,358.9		$ 131,470.6	$ 117,879.4
FTE adjustments	7.7		7.7		15.8	15.5
CORPORATE & INSTITUTIONAL SERVICES
Noninterest Income
Trust, Investment and Other Servicing Fees	566.2		549.4		1,140.6	1,084.6
Foreign Exchange Trading Income	68.3		57.3		153.4	117.0
Other Noninterest Income	69.0		44.8		110.8	88.2
Total Noninterest Income	703.5		651.5		1,404.8	1,289.8
Net Interest Income	165.4		229.6		376.7	464.4
Revenue	868.9		881.1		1,781.5	1,754.2
Provision for Credit Losses	28.8		(2.4)		54.5	(3.5)
Noninterest Expense	655.6		633.3		1,314.9	1,281.3
Income before Income Taxes	184.5		250.2		412.1	476.4
Provision for Income Taxes	41.3		58.3		91.2	111.9
Net Income	$ 143.2		$ 191.9		$ 320.9	$ 364.5
Percentage of Consolidated Net Income	45.00%		49.00%		48.00%	49.00%
Average Assets	$ 107,051.3		$ 86,696.3		$ 99,910.1	$ 88,512.4
WEALTH MANAGEMENT
Noninterest Income
Trust, Investment and Other Servicing Fees	395.3		406.1		824.5	799.8
Foreign Exchange Trading Income	3.0		3.2		6.8	9.7
Other Noninterest Income	40.8		31.5		83.2	57.0
Total Noninterest Income	439.1		440.8		914.5	866.5
Net Interest Income	214.4		195.5		419.3	390.5
Revenue	653.5		636.3		1,333.8	1,257.0
Provision for Credit Losses	37.2		(4.1)		72.5	(3.0)
Noninterest Expense	372.0		372.1		766.4	752.0
Income before Income Taxes	244.3		268.3		494.9	508.0
Provision for Income Taxes	60.8		67.9		121.7	128.7
Net Income	$ 183.5		$ 200.4		$ 373.2	$ 379.3
Percentage of Consolidated Net Income	59.00%		52.00%		55.00%	52.00%
Average Assets	$ 31,719.3		$ 29,662.6		$ 31,560.5	$ 29,367.0
TREASURY AND 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	(8.6)		(3.1)		(5.7)	(8.2)
Total Noninterest Income	(8.6)		(3.1)		(5.7)	(8.2)
Net Interest Income	0.0		0.0		0.0	0.0
Revenue	(8.6)		(3.1)		(5.7)	(8.2)
Provision for Credit Losses	0.0		0.0		0.0	0.0
Noninterest Expense	9.3		0.8		21.2	1.6
Income before Income Taxes	(17.9)		(3.9)		(26.9)	(9.8)
Provision for Income Taxes	(4.5)		(1.0)		(6.7)	(2.5)
Net Income	$ (13.4)		$ (2.9)		$ (20.2)	$ (7.3)
Percentage of Consolidated Net Income	(4.00%)		(1.00%)		(3.00%)	(1.00%)
Average Assets	$ 0.0		$ 0.0		$ 0.0	$ 0.0