PARENT COMPANY FINANCIALS - Condensed Statements of Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Income
Equity securities gains	$ 0	$ 1	$ 3
Total interest income	5,758	4,920	4,266
Operating expense
Salaries and employee benefits	1,880	1,766	1,714
Interest expense	1,226	747	508
All other expenses	495	542	521
Income taxes	462	260	489
NET INCOME	1,721	1,652	1,045
Other comprehensive income (loss), net of income taxes:
Net unrealized derivative instrument gains (losses) arising during the period	(33)	(14)	(62)
Net other comprehensive loss	(276)	(7)	(281)
Total other comprehensive loss, net of income taxes	(276)	(7)	(281)
Total comprehensive income	1,445	1,645	764
Parent company
Operating Income
Dividends from banking subsidiaries	1,650	1,055	555
Interest income	46	43	53
Management and service fees	22	31	26
Equity securities gains	0	1	3
All other operating income	1	1	7
Total interest income	1,726	1,136	644
Operating expense
Salaries and employee benefits	25	40	37
Interest expense	89	97	99
All other expenses	23	22	15
Total operating expense	137	159	151
Income before taxes and undistributed income	1,589	977	493
Income taxes	(13)	(10)	(26)
Income before undistributed income of subsidiaries and associated companies	1,602	987	519
Equity in undistributed income (losses) of subsidiaries and associated companies	120	665	526
NET INCOME	1,721	1,652	1,045
Other comprehensive income (loss), net of income taxes:
Net pension plan activity arising during the period	5	(1)	(2)
Net unrealized derivative instrument gains (losses) arising during the period	2	1	(8)
Net other comprehensive loss	7	0	(10)
Other comprehensive income (loss) activity of Bank subsidiaries, net of income taxes	(283)	(7)	(271)
Total other comprehensive loss, net of income taxes	(276)	(7)	(281)
Total comprehensive income	1,445	1,645	764
Nonbank subsidiaries | Parent company
Operating Income
Interest income	2	1	0
Dividends from nonbank subsidiaries	5	4	0
Operating expense
Equity in undistributed income (losses) of subsidiaries and associated companies	10	10	4
Bank subsidiaries | Parent company
Operating expense
Equity in undistributed income (losses) of subsidiaries and associated companies	$ 109	$ 655	$ 522