Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment							2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,003.8			$ 975.5			$ 2,968.9	$ 2,859.9
Foreign Exchange Trading Income	61.6			59.7			221.8	186.4
Other Noninterest Income	91.1			85.0			279.4	222.0
Total Noninterest Income	1,156.5			1,120.2			3,470.1	3,268.3
Net Interest Income	336.5			425.3			1,132.5	1,280.2
Revenue	1,493.0			1,545.5			4,602.6	4,548.5
Provision for Credit Losses	0.5			(7.0)			127.5	(13.5)
Noninterest Expense	1,094.7			1,036.3			3,197.2	3,071.2
Income before Income Taxes	397.8			516.2			1,277.9	1,490.8
Provision for Income Taxes	103.3			131.6			309.5	369.7
Net Income	$ 294.5	$ 313.3	$ 360.6	$ 384.6	$ 389.4	$ 347.1	$ 968.4	$ 1,121.1
Percentage of Consolidated Net Income	100.00%			100.00%			100.00%	100.00%
Average Assets	$ 140,925.4			$ 116,352.1			$ 134,645.2	$ 117,364.7
FTE adjustments	7.9			7.6			23.7	23.1
CORPORATE & INSTITUTIONAL SERVICES
Noninterest Income
Trust, Investment and Other Servicing Fees	584.9			559.9			1,725.5	1,644.5
Foreign Exchange Trading Income	58.4			55.5			211.8	172.5
Other Noninterest Income	56.7			53.6			167.5	141.8
Total Noninterest Income	700.0			669.0			2,104.8	1,958.8
Net Interest Income	139.9			229.9			516.6	694.3
Revenue	839.9			898.9			2,621.4	2,653.1
Provision for Credit Losses	(19.2)			4.8			35.3	1.3
Noninterest Expense	707.3			649.2			2,022.2	1,930.5
Income before Income Taxes	151.8			244.9			563.9	721.3
Provision for Income Taxes	38.7			59.9			129.9	171.8
Net Income	$ 113.1			$ 185.0			$ 434.0	$ 549.5
Percentage of Consolidated Net Income	39.00%			48.00%			45.00%	49.00%
Average Assets	$ 108,823.0			$ 85,982.2			$ 102,902.3	$ 87,664.1
WEALTH MANAGEMENT
Noninterest Income
Trust, Investment and Other Servicing Fees	418.9			415.6			1,243.4	1,215.4
Foreign Exchange Trading Income	3.2			4.2			10.0	13.9
Other Noninterest Income	39.7			38.1			122.9	95.1
Total Noninterest Income	461.8			457.9			1,376.3	1,324.4
Net Interest Income	196.6			195.4			615.9	585.9
Revenue	658.4			653.3			1,992.2	1,910.3
Provision for Credit Losses	19.7			(11.8)			92.2	(14.8)
Noninterest Expense	386.3			385.9			1,152.7	1,137.9
Income before Income Taxes	252.4			279.2			747.3	787.2
Provision for Income Taxes	66.2			73.6			187.9	202.3
Net Income	$ 186.2			$ 205.6			$ 559.4	$ 584.9
Percentage of Consolidated Net Income	63.00%			54.00%			58.00%	52.00%
Average Assets	$ 32,102.4			$ 30,369.9			$ 31,742.9	$ 29,700.6
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	(5.3)			(6.7)			(11.0)	(14.9)
Total Noninterest Income	(5.3)			(6.7)			(11.0)	(14.9)
Net Interest Income	0.0			0.0			0.0	0.0
Revenue	(5.3)			(6.7)			(11.0)	(14.9)
Provision for Credit Losses	0.0			0.0			0.0	0.0
Noninterest Expense	1.1			1.2			22.3	2.8
Income before Income Taxes	(6.4)			(7.9)			(33.3)	(17.7)
Provision for Income Taxes	(1.6)			(1.9)			(8.3)	(4.4)
Net Income	$ (4.8)			$ (6.0)			$ (25.0)	$ (13.3)
Percentage of Consolidated Net Income	(2.00%)			(2.00%)			(3.00%)	(1.00%)
Average Assets	$ 0.0			$ 0.0			$ 0.0	$ 0.0