BUSINESS OPERATING SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 1,121	$ 1,026	$ 2,212	$ 2,031
Noninterest income	388	370	759	749
Total revenue	1,509	1,396	2,971	2,780
Noninterest expense	875	864	1,758	1,718
Profit before provision for credit losses	634	532	1,213	1,062
Provision for credit losses	85	70	163	166
Income before income tax expense	549	462	1,050	896
Income tax expense	124	144	237	258
NET INCOME	425	318	813	638
Total average assets	153,253	149,878	152,393	149,335
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	759	657	1,492	1,295
Noninterest income	228	229	450	449
Total revenue	987	886	1,942	1,744
Noninterest expense	658	644	1,314	1,291
Profit before provision for credit losses	329	242	628	453
Provision for credit losses	66	60	138	124
Income before income tax expense	263	182	490	329
Income tax expense	66	64	123	116
NET INCOME	197	118	367	213
Total average assets	61,232	59,244	61,290	58,954
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	376	344	733	690
Noninterest income	140	130	265	264
Total revenue	516	474	998	954
Noninterest expense	200	192	408	382
Profit before provision for credit losses	316	282	590	572
Provision for credit losses	9	1	5	20
Income before income tax expense	307	281	585	552
Income tax expense	70	94	133	185
NET INCOME	237	187	452	367
Total average assets	52,170	49,731	51,286	49,488
Other Non-Segment
Segment Reporting Information [Line Items]
Net interest income	(14)	25	(13)	46
Noninterest income	20	11	44	36
Total revenue	6	36	31	82
Noninterest expense	17	28	36	45
Profit before provision for credit losses	(11)	8	(5)	37
Provision for credit losses	10	9	20	22
Income before income tax expense	(21)	(1)	(25)	15
Income tax expense	(12)	(14)	(19)	(43)
NET INCOME	(9)	13	(6)	58
Total average assets	$ 39,851	$ 40,903	$ 39,817	$ 40,893