PARENT COMPANY FINANCIALS - Condensed Statements of Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Income
Total interest income	$ 4,920	$ 4,266	$ 3,854
Operating expense
Salaries and employee benefits	1,761	1,709	1,636
Interest expense	747	508	452
All other expenses	547	526	530
Income taxes	260	489	423
NET INCOME	1,652	1,045	840
Other comprehensive (loss) income, net of income taxes
Net unrealized derivative instrument gains (losses) arising during the period	(14)	(62)	93
Net unrealized securities losses arising during the period	(6)	(139)	(66)
Total other comprehensive loss, net of income taxes	(7)	(281)	(15)
Total comprehensive income	1,645	764	825
Payments of ordinary common stock dividends	322	241	214
Dividends to preferred stockholders	14	14	7
Parent company
Operating Income
Dividends from banking subsidiaries	1,055	555	345
Interest income	43	53	54
Management and service fees	31	26	20
Equity securities gains	1	3	3
All other operating income	1	7	4
Total interest income	1,136	644	426
Operating expense
Salaries and employee benefits	40	37	15
Interest expense	97	99	108
All other expenses	22	15	38
Total operating expense	159	151	161
Income before taxes and undistributed income	977	493	265
Income taxes	(10)	(26)	(29)
Income before undistributed income of subsidiaries and associated companies	987	519	294
Equity in undistributed income (losses) of subsidiaries and associated companies	665	526	546
NET INCOME	1,652	1,045	840
Other comprehensive (loss) income, net of income taxes
Net pension plan activity arising during the period	(1)	(2)	1
Net unrealized derivative instrument gains (losses) arising during the period	1	(8)	2
Net unrealized securities losses arising during the period	0	0	(2)
Net other comprehensive loss	0	(10)	1
Other comprehensive income (loss) activity of Bank subsidiaries, net of income taxes	(7)	(271)	(16)
Total other comprehensive loss, net of income taxes	(7)	(281)	(15)
Total comprehensive income	1,645	764	825
Nonbank subsidiaries | Parent company
Operating Income
Interest income	1	0	0
Dividends from nonbank subsidiaries	4	0	0
Operating expense
Equity in undistributed income (losses) of subsidiaries and associated companies	10	4	3
Bank subsidiaries | Parent company
Operating expense
Equity in undistributed income (losses) of subsidiaries and associated companies	$ 655	$ 522	$ 543