Condensed Statement of Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING INCOME
Total Operating Income	$ 4,961.8	$ 4,702.6	$ 4,331.2
OPERATING EXPENSES
Interest Expense	182.0	153.9	181.4
Other Operating Expenses	364.4	328.0	272.1
Total Noninterest Expense	3,470.7	3,280.6	3,135.0
Benefit for Income Taxes	(484.6)	(491.2)	(378.4)
NET INCOME	1,032.5	973.8	811.8
Preferred Stock Dividends	23.4	23.4	9.5
Net Income Applicable to Common Stock	1,009.1	950.4	802.3
Parent Company
OPERATING INCOME
Intercompany Interest and Other Charges	39.8	38.5	42.9
Interest and Other Income	7.5	5.4	(0.3)
Total Operating Income	350.7	652.6	346.4
OPERATING EXPENSES
Interest Expense	63.5	59.3	66.6
Other Operating Expenses	19.9	56.8	17.0
Total Noninterest Expense	83.4	116.1	83.6
Income before Income Taxes and Equity in Undistributed Net Income of Subsidiaries	267.3	536.5	262.8
Benefit for Income Taxes	28.3	29.0	16.6
Income before Equity in Undistributed Net Income of Subsidiaries	295.6	565.5	279.4
Equity in Undistributed Net Income of Subsidiaries	736.9	408.3	532.4
NET INCOME	1,032.5	973.8	811.8
Preferred Stock Dividends	23.4	23.4	9.5
Net Income Applicable to Common Stock	1,009.1	950.4	802.3
Banks Industry | Parent Company
OPERATING INCOME
Dividends from Subsidiaries	300.0	600.0	300.0
OPERATING EXPENSES
Equity in Undistributed Net Income of Subsidiaries	708.3	392.8	522.1
Nonbank Subsidiaries | Parent Company
OPERATING INCOME
Dividends from Subsidiaries	3.4	8.7	3.8
OPERATING EXPENSES
Equity in Undistributed Net Income of Subsidiaries	$ 28.6	$ 15.5	$ 10.3