Condensed Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Cash on Deposit with Subsidiary Bank	$ 5,332.0	$ 6,418.5	$ 3,021.0	$ 3,159.0
Securities	44,501.2	37,567.4
Other Assets	4,953.8	4,464.4
Total Assets	123,926.9	116,749.6	109,946.5
LIABILITIES
Senior Notes	1,496.6	1,497.4
Floating Rate Capital Debt	277.4	277.3
Other Liabilities	3,611.9	3,075.6
Total Liabilities	114,156.5	108,043.7
STOCKHOLDERS’ EQUITY
Common Stock	408.6	408.6
Additional Paid-in Capital	1,035.8	1,072.3
Retained Earnings	8,908.4	8,242.8
Accumulated Other Comprehensive Income (Loss)	(370.0)	(372.7)
Treasury Stock	(1,094.4)	(1,033.6)
Total Stockholders’ Equity	9,770.4	8,705.9	8,448.9
Total Liabilities and Stockholders’ Equity	123,926.9	116,749.6
Parent Company
ASSETS
Cash on Deposit with Subsidiary Bank	757.0	757.5	$ 869.4	$ 1,566.4
Securities	0.9	1.2
Other Assets	599.1	682.3
Total Assets	12,750.3	11,800.7
LIABILITIES
Senior Notes	1,496.6	1,497.4
Long Term Debt	785.0	800.4
Floating Rate Capital Debt	277.4	277.3
Other Liabilities	420.9	519.7
Total Liabilities	2,979.9	3,094.8
STOCKHOLDERS’ EQUITY
Preferred Stock	882.0	388.5
Total Stockholders’ Equity	9,770.4	8,705.9
Total Liabilities and Stockholders’ Equity	12,750.3	11,800.7
Parent Company | Banks Industry
ASSETS
Advances to Wholly-Owned Subsidiaries	2,560.0	2,260.0
Investments in Wholly-Owned Subsidiaries	8,635.0	7,927.8
Parent Company | Nonbank Subsidiaries
ASSETS
Advances to Wholly-Owned Subsidiaries	13.5	18.5
Investments in Wholly-Owned Subsidiaries	$ 184.8	$ 153.4