PARENT COMPANY FINANCIALS - Condensed Cash Flow Statements (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES
Net income		$ 1,791	$ 1,721	$ 1,652
Deferred income taxes		64	97	(136)
Increase in other liabilities		331	303	(119)
Decrease (increase) in other assets		(856)	(1,217)	(502)
Net cash provided by operating activities		1,697	1,767	1,883
INVESTING ACTIVITIES
Net cash used in investing activities		(3,875)	(7,077)	(3,984)
FINANCING ACTIVITIES
Proceeds from issuance of long-term borrowed funds		12,850	22,503	15,363
Repayments of long-term borrowed funds		(14,857)	(14,837)	(12,751)
Treasury stock purchased		(1,220)	(1,025)	(820)
Net proceeds from issuance of preferred stock		730	593	0
Dividends declared and paid to preferred stockholders		(65)	(14)	(14)
Net cash provided by financing activities		1,490	6,352	1,429
(Decrease) increase in cash and cash equivalents		(688)	1,042	(672)	[1]
Cash and cash equivalents at beginning of period	[1]	4,074	3,032	3,704
Cash and cash equivalents at end of period	[1]	3,386	4,074	3,032
Parent company
OPERATING ACTIVITIES
Net income		1,791	1,721	1,652
Deferred income taxes		(8)	17	(11)
Gain on sales of assets		0	0	(1)
Equity in undistributed earnings of subsidiaries		(697)	(120)	(665)
Increase in other liabilities		50	11	99
Decrease (increase) in other assets		7	(7)	5
Other operating, net		58	40	(1)
Net cash provided by operating activities		1,201	1,662	1,078
INVESTING ACTIVITIES
Investments in and advances to subsidiaries		(105)	0	(230)
Repayment of investments in and advances to subsidiaries		55	0	167
Other investing, net		(1)	(1)	(1)
Net cash used in investing activities		(51)	(1)	(64)
FINANCING ACTIVITIES
Proceeds from issuance of long-term borrowed funds		500	0	0
Repayments of long-term borrowed funds		0	(333)	0
Proceeds from issuance of common stock		0	0	34
Treasury stock purchased		(1,220)	(1,025)	(820)
Net proceeds from issuance of preferred stock		730	593	0
Dividends declared and paid to common stockholders		(617)	(471)	(322)
Dividends declared and paid to preferred stockholders		(65)	(14)	(14)
Other financing, net		(21)	(13)	0
Net cash provided by financing activities		(693)	(1,263)	(1,122)
(Decrease) increase in cash and cash equivalents		457	398	(108)
Cash and cash equivalents at beginning of period		961	563	671
Cash and cash equivalents at end of period		$ 1,418	$ 961	$ 563

[1] Cash and cash equivalents include cash and due from banks and interest-bearing cash and due from banks as reflected on the Consolidated Balance Sheets.