Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment							2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,111.0			$ 1,003.8			$ 3,250.1	$ 2,968.9
Foreign Exchange Trading Income	66.4			61.6			215.7	221.8
Other Noninterest Income	110.0			91.1			309.6	279.4
Total Noninterest Income	1,287.4			1,156.5			3,775.4	3,470.1
Net Interest Income	357.1			336.5			1,047.7	1,132.5
Revenue	1,644.5			1,493.0			4,823.1	4,602.6
Provision for Credit Losses	(13.0)			0.5			(70.0)	127.5
Noninterest Expense	1,128.7			1,094.7			3,367.0	3,197.2
Income before Income Taxes	528.8			397.8			1,526.1	1,277.9
Provision for Income Taxes	133.1			103.3			387.2	309.5
Net Income	$ 395.7	$ 368.1	$ 375.1	$ 294.5	$ 313.3	$ 360.6	$ 1,138.9	$ 968.4
Percentage of Consolidated Net Income	100.00%			100.00%			100.00%	100.00%
Average Assets	$ 156,452.8			$ 140,925.4			$ 154,681.3	$ 134,645.2
FTE adjustments		$ 10.7		7.9			25.6	23.7
CORPORATE & INSTITUTIONAL SERVICES
Noninterest Income
Trust, Investment and Other Servicing Fees	630.2			584.9			1,862.2	1,725.5
Foreign Exchange Trading Income	63.2			58.4			205.6	211.8
Other Noninterest Income	65.6			56.7			194.8	167.5
Total Noninterest Income	759.0			700.0			2,262.6	2,104.8
Net Interest Income	158.9			139.9			472.7	516.6
Revenue	917.9			839.9			2,735.3	2,621.4
Provision for Credit Losses	(6.9)			(19.2)			(29.1)	35.3
Noninterest Expense	716.6			707.3			2,133.3	2,022.2
Income before Income Taxes	208.2			151.8			631.1	563.9
Provision for Income Taxes	50.0			38.7			153.1	129.9
Net Income	$ 158.2			$ 113.1			$ 478.0	$ 434.0
Percentage of Consolidated Net Income	40.00%			39.00%			42.00%	45.00%
Average Assets	$ 119,951.9			$ 108,823.0			$ 119,859.4	$ 102,902.3
WEALTH MANAGEMENT
Noninterest Income
Trust, Investment and Other Servicing Fees	480.8			418.9			1,387.9	1,243.4
Foreign Exchange Trading Income	3.2			3.2			10.1	10.0
Other Noninterest Income	48.0			39.7			130.5	122.9
Total Noninterest Income	532.0			461.8			1,528.5	1,376.3
Net Interest Income	198.2			196.6			575.0	615.9
Revenue	730.2			658.4			2,103.5	1,992.2
Provision for Credit Losses	(6.1)			19.7			(40.9)	92.2
Noninterest Expense	410.9			386.3			1,212.5	1,152.7
Income before Income Taxes	325.4			252.4			931.9	747.3
Provision for Income Taxes	84.3			66.2			243.3	187.9
Net Income	$ 241.1			$ 186.2			$ 688.6	$ 559.4
Percentage of Consolidated Net Income	61.00%			63.00%			60.00%	58.00%
Average Assets	$ 36,500.9			$ 32,102.4			$ 34,821.9	$ 31,742.9
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	(3.6)			(5.3)			(15.7)	(11.0)
Total Noninterest Income	(3.6)			(5.3)			(15.7)	(11.0)
Net Interest Income	0.0			0.0			0.0	0.0
Revenue	(3.6)			(5.3)			(15.7)	(11.0)
Provision for Credit Losses	0.0			0.0			0.0	0.0
Noninterest Expense	1.2			1.1			21.2	22.3
Income before Income Taxes	(4.8)			(6.4)			(36.9)	(33.3)
Provision for Income Taxes	(1.2)			(1.6)			(9.2)	(8.3)
Net Income	$ (3.6)			$ (4.8)			$ (27.7)	$ (25.0)
Percentage of Consolidated Net Income	(1.00%)			(2.00%)			(2.00%)	(3.00%)
Average Assets	$ 0.0			$ 0.0			$ 0.0	$ 0.0