Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) Segment	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | Segment							2
Trust, Investment and Other Servicing Fees	$ 975.5			$ 939.2			$ 2,859.9	$ 2,819.8
Foreign Exchange Trading Income	59.7			71.7			186.4	229.1
Other Noninterest Income	85.0			55.2			222.0	202.0
Net Interest Income	425.3			418.5			1,280.2	1,233.8
Revenue	1,545.5			1,484.6			4,548.5	4,484.7
Provision for Credit Losses	(7.0)			(9.0)			(13.5)	(10.5)
Noninterest Expense	1,036.3			1,002.3			3,071.2	2,995.0
Income before Income Taxes	516.2			491.3			1,490.8	1,500.2
Provision for Income Taxes	131.6			116.8			369.7	353.7
Net Income	$ 384.6	$ 389.4	$ 347.1	$ 374.5	$ 390.4	$ 381.6	$ 1,121.1	$ 1,146.5
Percentage of Consolidated Net Income	100.00%			100.00%			100.00%	100.00%
Average Assets	$ 116,352.1			$ 122,155.6			$ 117,364.7	$ 123,496.7
FTE adjustments	7.6			10.3			23.1	28.3
Corporate & Institutional Services
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	559.9			541.0			1,644.5	1,637.5
Foreign Exchange Trading Income	55.5			51.4			172.5	173.9
Other Noninterest Income	53.6			42.0			141.8	133.6
Net Interest Income	229.9			253.0			694.3	730.3
Revenue	898.9			887.4			2,653.1	2,675.3
Provision for Credit Losses	4.8			(2.8)			1.3	(3.7)
Noninterest Expense	649.2			601.0			1,930.5	1,785.9
Income before Income Taxes	244.9			289.2			721.3	893.1
Provision for Income Taxes	59.9			66.1			171.8	195.9
Net Income	$ 185.0			$ 223.1			$ 549.5	$ 697.2
Percentage of Consolidated Net Income	48.00%			59.00%			49.00%	61.00%
Average Assets	$ 85,982.2			$ 83,360.6			$ 87,664.1	$ 83,049.5
Wealth Management
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	415.6			398.2			1,215.4	1,182.3
Foreign Exchange Trading Income	4.2			0.9			13.9	3.1
Other Noninterest Income	38.1			25.5			95.1	77.9
Net Interest Income	195.4			202.9			585.9	611.3
Revenue	653.3			627.5			1,910.3	1,874.6
Provision for Credit Losses	(11.8)			(6.2)			(14.8)	(6.8)
Noninterest Expense	385.9			362.0			1,137.9	1,097.2
Income before Income Taxes	279.2			271.7			787.2	784.2
Provision for Income Taxes	73.6			67.2			202.3	193.7
Net Income	$ 205.6			$ 204.5			$ 584.9	$ 590.5
Percentage of Consolidated Net Income	54.00%			55.00%			52.00%	51.00%
Average Assets	$ 30,369.9			$ 26,110.5			$ 29,700.6	$ 26,101.6
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	0.0			19.4			0.0	52.1
Other Noninterest Income	(6.7)			(12.3)			(14.9)	(9.5)
Net Interest Income	0.0			(37.4)			0.0	(107.8)
Revenue	(6.7)			(30.3)			(14.9)	(65.2)
Provision for Credit Losses	0.0			0.0			0.0	0.0
Noninterest Expense	1.2			39.3			2.8	111.9
Income before Income Taxes	(7.9)			(69.6)			(17.7)	(177.1)
Provision for Income Taxes	(1.9)			(16.5)			(4.4)	(35.9)
Net Income	$ (6.0)			$ (53.1)			$ (13.3)	$ (141.2)
Percentage of Consolidated Net Income	(2.00%)			(14.00%)			(1.00%)	(12.00%)
Average Assets	$ 0.0			$ 12,684.5			$ 0.0	$ 14,345.6