Reporting Segments (Results of Reporting Segments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	$ 937.7	$ 808.2
Foreign Exchange Trading Income	78.5	48.1
Other Noninterest Income	75.8	74.6
Net Interest Income	392.7	362.4
Revenue	1,484.7	1,293.3
Provision for Credit Losses	(3.0)	(1.0)
Noninterest Expense	995.3	894.5
Income before Income Taxes	492.4	399.8
Provision for Income Taxes	110.8	123.7
Net Income	$ 381.6	$ 276.1
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 124,493.3	$ 116,476.4
FTE adjustments	8.7	8.9
Corporate & Institutional Services
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	544.3	462.9
Foreign Exchange Trading Income	62.4	49.1
Other Noninterest Income	46.6	44.2
Net Interest Income	229.4	166.5
Revenue	882.7	722.7
Provision for Credit Losses	(3.9)	0.3
Noninterest Expense	585.6	510.8
Income before Income Taxes	301.0	211.6
Provision for Income Taxes	66.8	66.9
Net Income	$ 234.2	$ 144.7
Percentage of Consolidated Net Income	61.00%	52.00%
Average Assets	$ 83,637.0	$ 77,803.5
Wealth Management
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	393.4	345.3
Foreign Exchange Trading Income	1.2	0.9
Other Noninterest Income	25.7	25.5
Net Interest Income	198.8	177.0
Revenue	619.1	548.7
Provision for Credit Losses	0.9	(1.3)
Noninterest Expense	365.7	346.3
Income before Income Taxes	252.5	203.7
Provision for Income Taxes	62.4	76.8
Net Income	$ 190.1	$ 126.9
Percentage of Consolidated Net Income	50.00%	46.00%
Average Assets	$ 26,108.0	$ 26,661.8
Treasury and Other
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	0.0	0.0
Foreign Exchange Trading Income	14.9	(1.9)
Other Noninterest Income	3.5	4.9
Net Interest Income	(35.5)	18.9
Revenue	(17.1)	21.9
Provision for Credit Losses	0.0	0.0
Noninterest Expense	44.0	37.4
Income before Income Taxes	(61.1)	(15.5)
Provision for Income Taxes	(18.4)	(20.0)
Net Income	$ (42.7)	$ 4.5
Percentage of Consolidated Net Income	(11.00%)	2.00%
Average Assets	$ 14,748.3	$ 12,011.1