Parent Company FInancial Statements Parent Company Financial Statements (Balance Sheets) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Cash and due from subsidiary bank	$ 973	$ 1,390
Other short-term investments	155	134
Premises and equipment	457	475
Accrued income and other assets	4,842	4,111
Total assets	73,402	70,818
Medium- and long-term debt	7,269	6,463
Other liabilities	1,440	1,243
Total liabilities	66,075	63,311
Common stock - $5 par value: Authorized - 325,000,000 shares; Issued - 228,164,824 shares	1,141	1,141
Capital surplus	2,174	2,148
Accumulated other comprehensive loss	(235)	(609)	$ (451)
Retained earnings	9,538	8,781
Less cost of common stock in treasury - 86,069,234 shares at 12/31/19 and 68,081,176 shares at 12/31/18	(5,291)	(3,954)
Total shareholders' equity	7,327	7,507	$ 7,963	$ 7,796
Total liabilities and shareholders' equity	$ 73,402	$ 70,818
Common stock, par value	$ 5	$ 5
Common stock, authorized shares	325,000,000	325,000,000
Common stock, issued shares	228,164,824	228,164,824
Shares in treasury	86,069,234	68,081,176
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash and due from subsidiary bank	$ 1,196	$ 1,524
Other short-term investments	95	88
Investments in subsidiaries, principally banks	7,784	7,429
Premises and equipment	1	1
Accrued income and other assets	242	169
Total assets	9,318	9,211
Medium- and long-term debt	1,735	1,459
Other liabilities	256	245
Total liabilities	1,991	1,704
Common stock - $5 par value: Authorized - 325,000,000 shares; Issued - 228,164,824 shares	1,141	1,141
Capital surplus	2,174	2,148
Accumulated other comprehensive loss	(235)	(609)
Retained earnings	9,538	8,781
Less cost of common stock in treasury - 86,069,234 shares at 12/31/19 and 68,081,176 shares at 12/31/18	(5,291)	(3,954)
Total shareholders' equity	7,327	7,507
Total liabilities and shareholders' equity	$ 9,318	$ 9,211