Reporting Segments (Results of Reporting Segments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	$ 867.9	$ 788.3	$ 2,524.3	$ 2,313.7
Foreign Exchange Trading Income	49.1	53.6	147.1	178.5
Other Noninterest Income	74.0	68.7	230.2	317.6
Net Interest Income	366.2	310.1	1,079.0	930.7
Revenue	1,357.2	1,220.7	3,980.6	3,740.5
Provision for Credit Losses	(7.0)	(3.0)	(15.0)	(4.0)
Noninterest Expense	935.6	843.0	2,767.5	2,596.8
Income before Income Taxes	428.6	380.7	1,228.1	1,147.7
Provision for Income Taxes	130.2	123.1	385.7	381.7
Net Income	$ 298.4	$ 257.6	$ 842.4	$ 766.0
Percentage of Consolidated Net Income	100.00%	100.00%	100.00%	100.00%
Average Assets	$ 121,159.4	$ 116,382.5	$ 118,696.0	$ 114,909.9
FTE adjustments	12.0	7.0	29.8	20.1
Corporate & Institutional Services
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	501.1	450.8	1,451.1	1,331.1
Foreign Exchange Trading Income	47.2	55.2	146.9	169.1
Other Noninterest Income	43.8	41.5	132.4	113.0
Net Interest Income	194.0	138.2	536.5	417.8
Revenue	786.1	685.7	2,266.9	2,031.0
Provision for Credit Losses	0.8	4.0	(1.6)	0.0
Noninterest Expense	542.1	487.8	1,598.5	1,519.9
Income before Income Taxes	243.2	193.9	670.0	511.1
Provision for Income Taxes	78.4	61.8	213.0	158.0
Net Income	$ 164.8	$ 132.1	$ 457.0	$ 353.1
Percentage of Consolidated Net Income	55.00%	51.00%	54.00%	46.00%
Average Assets	$ 82,250.9	$ 75,696.5	$ 80,229.1	$ 75,589.0
Wealth Management
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	366.8	337.5	1,073.2	982.6
Foreign Exchange Trading Income	0.7	0.9	2.4	7.0
Other Noninterest Income	25.2	26.3	77.4	79.8
Net Interest Income	186.6	164.1	545.4	482.8
Revenue	579.3	528.8	1,698.4	1,552.2
Provision for Credit Losses	(7.8)	(7.0)	(13.4)	(4.0)
Noninterest Expense	348.8	318.0	1,046.0	975.2
Income before Income Taxes	238.3	217.8	665.8	581.0
Provision for Income Taxes	90.3	82.3	251.4	219.1
Net Income	$ 148.0	$ 135.5	$ 414.4	$ 361.9
Percentage of Consolidated Net Income	50.00%	53.00%	49.00%	47.00%
Average Assets	$ 26,463.0	$ 26,601.7	$ 26,648.7	$ 26,525.6
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	1.2	(2.5)	(2.2)	2.4
Other Noninterest Income	5.0	0.9	20.4	124.8
Net Interest Income	(14.4)	7.8	(2.9)	30.1
Revenue	(8.2)	6.2	15.3	157.3
Provision for Credit Losses	0.0	0.0	0.0	0.0
Noninterest Expense	44.7	37.2	123.0	101.7
Income before Income Taxes	(52.9)	(31.0)	(107.7)	55.6
Provision for Income Taxes	(38.5)	(21.0)	(78.7)	4.6
Net Income	$ (14.4)	$ (10.0)	$ (29.0)	$ 51.0
Percentage of Consolidated Net Income	(5.00%)	(4.00%)	(3.00%)	7.00%
Average Assets	$ 12,445.5	$ 14,084.3	$ 11,818.2	$ 12,795.3