Condensed Statement of Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
OPERATING INCOME
Total Operating Income	$ 4,331.2	[1]	$ 4,089.3	[1]	$ 3,896.1	[1]
OPERATING EXPENSES
Interest Expense	181.4		222.4		297.4
Other Operating Expenses	272.1		314.2		282.9
Total Noninterest Expense	3,135.0		2,993.8		2,878.8
Benefit for Income Taxes	(378.4)		(344.2)		(305.0)
NET INCOME	811.8		731.3		687.3
Preferred Stock Dividends	9.5
Net Income Applicable to Common Stock	802.3		731.3		687.3
Parent Company
OPERATING INCOME
Intercompany Interest and Other Charges	42.9		33.2		30.0
Interest and Other Income	(0.3)		9.0		10.6
Total Operating Income	346.4		943.9		506.8
OPERATING EXPENSES
Interest Expense	66.6		78.3		74.9
Other Operating Expenses	17.0		20.8		13.0
Total Noninterest Expense	83.6		99.1		87.9
Income before Income Taxes and Equity in Undistributed Net Income of Subsidiaries	262.8		844.8		418.9
Benefit for Income Taxes	16.6		24.2		21.1
Income before Equity in Undistributed Net Income of Subsidiaries	279.4		869.0		440.0
Equity in Undistributed Net Income of Subsidiaries	532.4		(131.0)		247.3
NET INCOME	811.8		731.3		687.3
Preferred Stock Dividends	9.5
Net Income Applicable to Common Stock	802.3		731.3		687.3
Parent Company | Banks Industry
OPERATING INCOME
Dividends from Subsidiaries	300.0		880.0		440.0
OPERATING EXPENSES
Equity in Undistributed Net Income of Subsidiaries	522.1		(152.5)		266.9
Parent Company | Nonbank Subsidiaries
OPERATING INCOME
Dividends from Subsidiaries	3.8		21.7		26.2
OPERATING EXPENSES
Equity in Undistributed Net Income of Subsidiaries	$ 10.3		$ 14.8		$ (19.6)

[1] Total revenue is comprised of net interest income and noninterest income.