Reporting Segments (Results of Reporting Segments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	$ 942.9	$ 848.2	$ 1,880.6	$ 1,656.4
Foreign Exchange Trading Income	78.9	49.9	157.4	98.0
Other Noninterest Income	71.0	81.6	146.8	156.2
Net Interest Income	422.6	350.4	815.3	712.8
Revenue	1,515.4	1,330.1	3,000.1	2,623.4
Provision for Credit Losses	1.5	(7.0)	(1.5)	(8.0)
Noninterest Expense	997.4	937.4	1,992.7	1,831.9
Income before Income Taxes	516.5	399.7	1,008.9	799.5
Provision for Income Taxes	126.1	131.8	236.9	255.5
Net Income	$ 390.4	$ 267.9	$ 772.0	$ 544.0
Percentage of Consolidated Net Income	100.00%	100.00%	100.00%	100.00%
Average Assets	$ 123,866.7	$ 118,400.7	$ 124,178.3	$ 117,443.8
FTE adjustments	9.3	8.9	18.0	17.8
Corporate & Institutional Services
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	552.2	487.1	1,096.5	950.0
Foreign Exchange Trading Income	60.1	50.6	122.5	99.7
Other Noninterest Income	45.0	44.4	91.6	88.6
Net Interest Income	247.9	176.0	477.3	342.5
Revenue	905.2	758.1	1,787.9	1,480.8
Provision for Credit Losses	3.0	(2.7)	(0.9)	(2.4)
Noninterest Expense	599.3	545.6	1,184.9	1,056.4
Income before Income Taxes	302.9	215.2	603.9	426.8
Provision for Income Taxes	63.0	67.7	129.8	134.6
Net Income	$ 239.9	$ 147.5	$ 474.1	$ 292.2
Percentage of Consolidated Net Income	62.00%	55.00%	61.00%	54.00%
Average Assets	$ 82,153.1	$ 80,584.0	$ 82,891.4	$ 79,201.4
Wealth Management
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	390.7	361.1	784.1	706.4
Foreign Exchange Trading Income	1.0	0.8	2.2	1.7
Other Noninterest Income	26.7	26.7	52.4	52.2
Net Interest Income	209.6	181.8	408.4	358.8
Revenue	628.0	570.4	1,247.1	1,119.1
Provision for Credit Losses	(1.5)	(4.3)	(0.6)	(5.6)
Noninterest Expense	369.5	350.9	735.2	697.2
Income before Income Taxes	260.0	223.8	512.5	427.5
Provision for Income Taxes	64.1	84.3	126.5	161.1
Net Income	$ 195.9	$ 139.5	$ 386.0	$ 266.4
Percentage of Consolidated Net Income	50.00%	52.00%	50.00%	49.00%
Average Assets	$ 26,086.3	$ 26,823.5	$ 26,097.1	$ 26,743.1
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	17.8	(1.5)	32.7	(3.4)
Other Noninterest Income	(0.7)	10.5	2.8	15.4
Net Interest Income	(34.9)	(7.4)	(70.4)	11.5
Revenue	(17.8)	1.6	(34.9)	23.5
Provision for Credit Losses	0.0	0.0	0.0	0.0
Noninterest Expense	28.6	40.9	72.6	78.3
Income before Income Taxes	(46.4)	(39.3)	(107.5)	(54.8)
Provision for Income Taxes	(1.0)	(20.2)	(19.4)	(40.2)
Net Income	$ (45.4)	$ (19.1)	$ (88.1)	$ (14.6)
Percentage of Consolidated Net Income	(12.00%)	(7.00%)	(11.00%)	(3.00%)
Average Assets	$ 15,627.3	$ 10,993.2	$ 15,189.8	$ 11,499.3