Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Segment	Jun. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | Segment			2
Trust, Investment and Other Servicing Fees	$ 955.5	$ 942.9	$ 1,884.4	$ 1,880.6
Foreign Exchange Trading Income	60.5	78.9	126.7	157.4
Other Noninterest Income	73.2	71.0	137.0	146.8
Net Interest Income	425.1	422.6	854.9	815.3
Revenue	1,514.3	1,515.4	3,003.0	3,000.1
Provision for Credit Losses	(6.5)	1.5	(6.5)	(1.5)
Noninterest Expense	1,006.2	997.4	2,034.9	1,992.7
Income before Income Taxes	514.6	516.5	974.6	1,008.9
Provision for Income Taxes	125.2	126.1	238.1	236.9
Net Income	$ 389.4	$ 390.4	$ 736.5	$ 772.0
Percentage of Consolidated Net Income	100.00%	100.00%	100.00%	100.00%
Average Assets	$ 116,358.9	$ 123,866.7	$ 117,879.4	$ 124,178.3
FTE adjustments	7.7	9.3	15.5	18.0
Corporate & Institutional Services
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	549.4	552.2	1,084.6	1,096.5
Foreign Exchange Trading Income	57.3	60.1	117.0	122.5
Other Noninterest Income	44.8	45.0	88.2	91.6
Net Interest Income	229.6	247.9	464.4	477.3
Revenue	881.1	905.2	1,754.2	1,787.9
Provision for Credit Losses	(2.4)	3.0	(3.5)	(0.9)
Noninterest Expense	633.3	599.3	1,281.3	1,184.9
Income before Income Taxes	250.2	302.9	476.4	603.9
Provision for Income Taxes	58.3	63.0	111.9	129.8
Net Income	$ 191.9	$ 239.9	$ 364.5	$ 474.1
Percentage of Consolidated Net Income	49.00%	62.00%	49.00%	61.00%
Average Assets	$ 86,696.3	$ 82,153.1	$ 88,512.4	$ 82,891.4
Wealth Management
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	406.1	390.7	799.8	784.1
Foreign Exchange Trading Income	3.2	1.0	9.7	2.2
Other Noninterest Income	31.5	26.7	57.0	52.4
Net Interest Income	195.5	209.6	390.5	408.4
Revenue	636.3	628.0	1,257.0	1,247.1
Provision for Credit Losses	(4.1)	(1.5)	(3.0)	(0.6)
Noninterest Expense	372.1	369.5	752.0	735.2
Income before Income Taxes	268.3	260.0	508.0	512.5
Provision for Income Taxes	67.9	64.1	128.7	126.5
Net Income	$ 200.4	$ 195.9	$ 379.3	$ 386.0
Percentage of Consolidated Net Income	52.00%	50.00%	52.00%	50.00%
Average Assets	$ 29,662.6	$ 26,086.3	$ 29,367.0	$ 26,097.1
Treasury and Other
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	0.0	0.0	0.0	0.0
Foreign Exchange Trading Income	0.0	17.8	0.0	32.7
Other Noninterest Income	(3.1)	(0.7)	(8.2)	2.8
Net Interest Income	0.0	(34.9)	0.0	(70.4)
Revenue	(3.1)	(17.8)	(8.2)	(34.9)
Provision for Credit Losses	0.0	0.0	0.0	0.0
Noninterest Expense	0.8	28.6	1.6	72.6
Income before Income Taxes	(3.9)	(46.4)	(9.8)	(107.5)
Provision for Income Taxes	(1.0)	(1.0)	(2.5)	(19.4)
Net Income	$ (2.9)	$ (45.4)	$ (7.3)	$ (88.1)
Percentage of Consolidated Net Income	(1.00%)	(12.00%)	(1.00%)	(11.00%)
Average Assets	$ 0.0	$ 15,627.3	$ 0.0	$ 15,189.8