PARENT COMPANY FINANCIALS - Condensed Cash Flow Statements (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
OPERATING ACTIVITIES
Net income		$ 1,721	$ 1,652	$ 1,045
Deferred income taxes		97	(136)	153
Increase (decrease) in other liabilities		303	(119)	(59)
(Increase) decrease in other assets		(1,217)	(502)	(274)
Net cash provided by operating activities		1,767	1,883	1,490
INVESTING ACTIVITIES
Net cash used in investing activities		(7,077)	(3,984)	(11,326)
FINANCING ACTIVITIES
Proceeds from issuance of long-term borrowed funds		22,503	15,363	15,144
Repayments of long-term borrowed funds		(14,837)	(12,751)	(8,429)
Treasury stock purchased		(1,025)	(820)	(430)
Net proceeds from issuance of preferred stock		593	0	0
Dividends declared and paid to common stockholders		(471)	(322)	(241)
Dividends declared and paid to preferred stockholders		(14)	(14)	(14)
Net cash provided by financing activities		6,352	1,429	10,455
Increase (Decrease) in cash and cash equivalents	[1]	1,042	(672)	619
Cash and cash equivalents at beginning of period	[1]	3,032	3,704	3,085
Cash and cash equivalents at end of period	[1]	4,074	3,032	3,704
Parent company
OPERATING ACTIVITIES
Net income		1,721	1,652	1,045
Deferred income taxes		17	(11)	5
Gain on sales of assets		0	(1)	(3)
Equity in undistributed earnings of subsidiaries		(120)	(665)	(526)
Increase (decrease) in other liabilities		11	99	(19)
(Increase) decrease in other assets		(7)	5	35
Other operating, net		40	(1)	(4)
Total adjustments		(59)	(574)	(512)
Net cash provided by operating activities		1,662	1,078	533
INVESTING ACTIVITIES
Investments in and advances to subsidiaries		0	(230)	(40)
Repayment of investments in and advances to subsidiaries		0	167	588
Other investing, net		(1)	(1)	(2)
Net cash used in investing activities		(1)	(64)	546
FINANCING ACTIVITIES
Proceeds from issuance of long-term borrowed funds		0	0	349
Repayments of long-term borrowed funds		(333)	0	(625)
Proceeds from issuance of common stock		0	34	22
Treasury stock purchased		(1,025)	(820)	(430)
Net proceeds from issuance of preferred stock		593	0	0
Dividends declared and paid to common stockholders		(471)	(322)	(241)
Dividends declared and paid to preferred stockholders		(14)	(14)	(14)
Other financing, net		(13)	0	0
Net cash provided by financing activities		(1,263)	(1,122)	(939)
Increase (Decrease) in cash and cash equivalents		398	(108)	140
Cash and cash equivalents at beginning of period		563	671	531
Cash and cash equivalents at end of period		$ 961	$ 563	$ 671

[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.