Reporting Segments (Results of Reporting Segments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	$ 939.2	$ 867.9	$ 2,819.8	$ 2,524.3
Foreign Exchange Trading Income	71.7	49.1	229.1	147.1
Other Noninterest Income	55.2	74.0	202.0	230.2
Net Interest Income	418.5	366.2	1,233.8	1,079.0
Revenue	1,484.6	1,357.2	4,484.7	3,980.6
Provision for Credit Losses	(9.0)	(7.0)	(10.5)	(15.0)
Noninterest Expense	1,002.3	935.6	2,995.0	2,767.5
Income before Income Taxes	491.3	428.6	1,500.2	1,228.1
Provision for Income Taxes	116.8	130.2	353.7	385.7
Net Income	$ 374.5	$ 298.4	$ 1,146.5	$ 842.4
Percentage of Consolidated Net Income	100.00%	100.00%	100.00%	100.00%
Average Assets	$ 122,155.6	$ 121,159.4	$ 123,496.7	$ 118,696.0
FTE adjustments	10.3	12.0	28.3	29.8
Corporate & Institutional Services
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	541.0	501.1	1,637.5	1,451.1
Foreign Exchange Trading Income	51.4	47.2	173.9	146.9
Other Noninterest Income	42.0	43.8	133.6	132.4
Net Interest Income	253.0	194.0	730.3	536.5
Revenue	887.4	786.1	2,675.3	2,266.9
Provision for Credit Losses	(2.8)	0.8	(3.7)	(1.6)
Noninterest Expense	601.0	542.1	1,785.9	1,598.5
Income before Income Taxes	289.2	243.2	893.1	670.0
Provision for Income Taxes	66.1	78.4	195.9	213.0
Net Income	$ 223.1	$ 164.8	$ 697.2	$ 457.0
Percentage of Consolidated Net Income	59.00%	55.00%	61.00%	54.00%
Average Assets	$ 83,360.6	$ 82,250.9	$ 83,049.5	$ 80,229.1
Wealth Management
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	398.2	366.8	1,182.3	1,073.2
Foreign Exchange Trading Income	0.9	0.7	3.1	2.4
Other Noninterest Income	25.5	25.2	77.9	77.4
Net Interest Income	202.9	186.6	611.3	545.4
Revenue	627.5	579.3	1,874.6	1,698.4
Provision for Credit Losses	(6.2)	(7.8)	(6.8)	(13.4)
Noninterest Expense	362.0	348.8	1,097.2	1,046.0
Income before Income Taxes	271.7	238.3	784.2	665.8
Provision for Income Taxes	67.2	90.3	193.7	251.4
Net Income	$ 204.5	$ 148.0	$ 590.5	$ 414.4
Percentage of Consolidated Net Income	55.00%	50.00%	51.00%	49.00%
Average Assets	$ 26,110.5	$ 26,463.0	$ 26,101.6	$ 26,648.7
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	19.4	1.2	52.1	(2.2)
Other Noninterest Income	(12.3)	5.0	(9.5)	20.4
Net Interest Income	(37.4)	(14.4)	(107.8)	(2.9)
Revenue	(30.3)	(8.2)	(65.2)	15.3
Provision for Credit Losses	0.0	0.0	0.0	0.0
Noninterest Expense	39.3	44.7	111.9	123.0
Income before Income Taxes	(69.6)	(52.9)	(177.1)	(107.7)
Provision for Income Taxes	(16.5)	(38.5)	(35.9)	(78.7)
Net Income	$ (53.1)	$ (14.4)	$ (141.2)	$ (29.0)
Percentage of Consolidated Net Income	(14.00%)	(5.00%)	(12.00%)	(3.00%)
Average Assets	$ 12,684.5	$ 12,445.5	$ 14,345.6	$ 11,818.2