Condensed Statement of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING ACTIVITIES:
Net Income	$ 973.8	$ 811.8	$ 731.3
Adjustments to Reconcile Net Income to Net Cash Provided by (Used in) Operating Activities:
Change in Accrued Income Taxes	206.8	55.2	(31.5)
Other, net	(318.1)	86.1	176.9
Net Cash Provided by Operating Activities	1,834.4	936.0	839.3
INVESTING ACTIVITIES:
Change in Time Deposits with Banks	(144.9)	3,297.2	(782.1)
Purchases of Securities – Available for Sale	(11,490.3)	(12,668.0)	(8,168.0)
Proceeds from Sale, Maturity and Redemption of Securities – Available for Sale	8,576.1	11,476.6	8,456.4
Other, net	(212.9)	(157.4)	109.4
Net Cash Used in Investing Activities	(6,900.7)	(8,212.4)	(5,683.3)
FINANCING ACTIVITIES:
Change in Senior Notes and Long-Term Debt	0.0	0.0	750.0
Proceeds from Issuance of Preferred Stock – Series C	0.0	388.5	0.0
Treasury Stock Purchased	(496.9)	(480.7)	(309.7)
Net Proceeds from Stock Options	94.0	127.5	146.2
Cash Dividends Paid on Common Stock	(321.4)	(302.9)	(220.6)
Cash Dividends Paid on Preferred Stock	(27.0)	0.0	0.0
Other, net	17.8	(222.4)	226.7
Net Cash Provided by Financing Activities	8,534.1	7,073.7	4,388.3
Increase (Decrease) in Cash and Due from Banks	3,394.0	(111.8)	(590.3)
Cash and Due from Banks at Beginning of Year	3,050.6	3,162.4	3,752.7
Cash and Due from Banks at End of Year	6,444.6	3,050.6	3,162.4
Parent Company
OPERATING ACTIVITIES:
Net Income	973.8	811.8	731.3
Adjustments to Reconcile Net Income to Net Cash Provided by (Used in) Operating Activities:
Equity in Undistributed Net Income of Subsidiaries	(408.3)	(532.4)	131.0
Change in Prepaid Expenses	1.2	0.2	(1.1)
Change in Accrued Income Taxes	22.8	(30.7)	(18.1)
Other, net	58.4	56.1	102.6
Net Cash Provided by Operating Activities	647.9	305.0	945.7
INVESTING ACTIVITIES:
Change in Time Deposits with Banks	0.0	0.0	1,691.4
Purchases of Securities – Available for Sale	0.0	0.0	0.0
Proceeds from Sale, Maturity and Redemption of Securities – Available for Sale	1.3	2.9	0.2
Change in Capital Investments in Subsidiaries	(10.0)	0.0	(13.0)
Advances to Wholly-Owned Subsidiaries	0.0	(238.5)	(1,000.0)
Other, net	0.2	1.1	1.8
Net Cash Used in Investing Activities	(8.5)	(234.5)	680.4
FINANCING ACTIVITIES:
Change in Senior Notes and Long-Term Debt	0.0	(500.0)	317.9
Proceeds from Issuance of Preferred Stock – Series C	0.0	388.5	0.0
Treasury Stock Purchased	(496.9)	(480.7)	(309.7)
Net Proceeds from Stock Options	94.0	127.5	146.2
Cash Dividends Paid on Common Stock	(321.4)	(302.9)	(220.6)
Cash Dividends Paid on Preferred Stock	(27.0)	0.0	0.0
Other, net	0.0	0.1	0.0
Net Cash Provided by Financing Activities	(751.3)	(767.5)	(66.2)
Increase (Decrease) in Cash and Due from Banks	(111.9)	(697.0)	1,559.9
Cash and Due from Banks at Beginning of Year	869.4	1,566.4	6.5
Cash and Due from Banks at End of Year	$ 757.5	$ 869.4	$ 1,566.4