Condensed Statement of Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING INCOME
Total Operating Income	$ 4,702.6	$ 4,331.2	$ 4,089.3
OPERATING EXPENSES
Interest Expense	153.9	181.4	222.4
Other Operating Expenses	328.0	272.1	314.2
Total Noninterest Expense	3,280.6	3,135.0	2,993.8
Benefit for Income Taxes	(491.2)	(378.4)	(344.2)
NET INCOME	973.8	811.8	731.3
Preferred Stock Dividends	23.4	9.5	0.0
Net Income Applicable to Common Stock	950.4	802.3	731.3
Parent Company
OPERATING INCOME
Intercompany Interest and Other Charges	38.5	42.9	33.2
Interest and Other Income	5.4	(0.3)	9.0
Total Operating Income	652.6	346.4	943.9
OPERATING EXPENSES
Interest Expense	59.3	66.6	78.3
Other Operating Expenses	56.8	17.0	20.8
Total Noninterest Expense	116.1	83.6	99.1
Income before Income Taxes and Equity in Undistributed Net Income of Subsidiaries	536.5	262.8	844.8
Benefit for Income Taxes	29.0	16.6	24.2
Income before Equity in Undistributed Net Income of Subsidiaries	565.5	279.4	869.0
Equity in Undistributed Net Income of Subsidiaries	408.3	532.4	(131.0)
NET INCOME	973.8	811.8	731.3
Preferred Stock Dividends	23.4	9.5	0.0
Net Income Applicable to Common Stock	950.4	802.3	731.3
Nonbank Subsidiaries | Parent Company
OPERATING INCOME
Dividends from Subsidiaries	8.7	3.8	21.7
OPERATING EXPENSES
Equity in Undistributed Net Income of Subsidiaries	15.5	10.3	14.8
Banks Industry | Parent Company
OPERATING INCOME
Dividends from Subsidiaries	600.0	300.0	880.0
OPERATING EXPENSES
Equity in Undistributed Net Income of Subsidiaries	$ 392.8	$ 522.1	$ (152.5)