BUSINESS OPERATING SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 1,148	$ 1,062	$ 3,360	$ 3,093
Noninterest income	416	381	1,175	1,130
Total revenue	1,564	1,443	4,535	4,223
Noninterest expense	910	858	2,668	2,576
Profit (loss) before provision for credit losses	654	585	1,867	1,647
Provision for credit losses	78	72	241	238
Income before income tax expense	576	513	1,626	1,409
Income tax expense (benefit)	133	165	370	423
NET INCOME	443	348	1,256	986
Total average assets	155,624	150,012	153,482	149,563
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	776	674	2,268	1,969
Noninterest income	258	227	708	676
Total revenue	1,034	901	2,976	2,645
Noninterest expense	686	648	2,000	1,939
Profit (loss) before provision for credit losses	348	253	976	706
Provision for credit losses	71	65	209	189
Income before income tax expense	277	188	767	517
Income tax expense (benefit)	70	66	193	182
NET INCOME	207	122	574	335
Total average assets	62,974	60,012	61,857	59,310
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	380	354	1,113	1,044
Noninterest income	140	136	405	400
Total revenue	520	490	1,518	1,444
Noninterest expense	202	195	610	577
Profit (loss) before provision for credit losses	318	295	908	867
Provision for credit losses	14	0	19	20
Income before income tax expense	304	295	889	847
Income tax expense (benefit)	70	94	203	279
NET INCOME	234	201	686	568
Total average assets	52,871	49,833	51,820	49,604
Other
Segment Reporting Information [Line Items]
Net interest income	(8)	34	(21)	80
Noninterest income	18	18	62	54
Total revenue	10	52	41	134
Noninterest expense	22	15	58	60
Profit (loss) before provision for credit losses	(12)	37	(17)	74
Provision for credit losses	(7)	7	13	29
Income before income tax expense	(5)	30	(30)	45
Income tax expense (benefit)	(7)	5	(26)	(38)
NET INCOME	2	25	(4)	83
Total average assets	$ 39,779	$ 40,167	$ 39,805	$ 40,649