Condensed Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
ASSETS
Cash on Deposit with Subsidiary Bank	$ 3,050.6		$ 3,162.4		$ 3,752.7	$ 4,315.3
Securities	33,734.0		30,720.3
Buildings and Equipment	444.3		458.8
Other Assets	5,865.1		4,764.0
Total Assets	109,946.5		102,947.3		97,463.8
LIABILITIES
Senior Notes	1,497.0	[1],[2]	1,996.6	[1],[2]
Long Term Debt	1,615.1		1,709.2
Floating Rate Capital Debt	277.2		277.1
Other Liabilities	3,848.1		3,513.3
Total Liabilities	101,497.6		95,035.3
STOCKHOLDERS' EQUITY
Preferred Stock	388.5
Common Stock	408.6		408.6
Retained Earnings	7,625.4		7,134.8
Accumulated Other Comprehensive Loss	(319.7)		(244.3)		(283.0)	(345.6)
Treasury Stock	(704.8)		(422.8)
Total Stockholders' Equity	8,448.9		7,912.0		7,527.0
Total Liabilities and Stockholders' Equity	109,946.5		102,947.3
Parent Company
ASSETS
Cash on Deposit with Subsidiary Bank	869.4		1,566.4		6.5	6.5
Time Deposits with Subsidiary Banks	0		0
Securities	2.3		5.3
Buildings and Equipment	0		0
Other Assets	605.8		608.8
Total Assets	11,483.5		11,490.7
LIABILITIES
Senior Notes	1,497.0		1,996.6
Long Term Debt	793.0		717.8
Floating Rate Capital Debt	277.2		277.1
Other Liabilities	467.4		587.2
Total Liabilities	3,034.6		3,578.7
STOCKHOLDERS' EQUITY
Preferred Stock	388.5
Common Stock	408.6		408.6
Additional Paid-in Capital	1,050.9		1,035.7
Retained Earnings	7,625.4		7,134.8
Accumulated Other Comprehensive Loss	(319.7)		(244.3)
Treasury Stock	(704.8)		(422.8)
Total Stockholders' Equity	8,448.9		7,912.0
Total Liabilities and Stockholders' Equity	11,483.5		11,490.7
Parent Company | Banks Industry
ASSETS
Advances to Wholly-Owned Subsidiaries	2,273.5		2,035.0
Investments in Wholly-Owned Subsidiaries	7,604.5		7,101.7
Parent Company | Nonbank Subsidiaries
ASSETS
Advances to Wholly-Owned Subsidiaries	5.0		5.0
Investments in Wholly-Owned Subsidiaries	$ 123.0		$ 168.5

[1] Not redeemable prior to maturity.

[2] Debt issue costs are recorded as an asset and amortized on a straight-line basis over the life of the Note.