BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Net interest income	$ 1,062	$ 945	$ 3,093	$ 2,772
Noninterest income	381	435	1,130	1,120
Total revenue	1,443	1,380	4,223	3,892
Noninterest expense	858	867	2,576	2,505
Profit before provision for credit losses	585	513	1,647	1,387
Provision for credit losses	72	86	238	267
Income before income tax expense	513	427	1,409	1,120
Income tax expense	165	130	423	357
NET INCOME	348	297	986	763
Total average assets	150,012	144,399	149,563	141,795
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	674	621	1,969	1,804
Noninterest income	227	229	676	656
Total revenue	901	850	2,645	2,460
Noninterest expense	648	650	1,939	1,898
Profit before provision for credit losses	253	200	706	562
Provision for credit losses	65	57	189	169
Income before income tax expense	188	143	517	393
Income tax expense	66	51	182	140
NET INCOME	122	92	335	253
Total average assets	60,012	56,689	59,310	55,825
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	354	327	1,044	941
Noninterest income	136	123	400	344
Total revenue	490	450	1,444	1,285
Noninterest expense	195	181	577	554
Profit before provision for credit losses	295	269	867	731
Provision for credit losses	0	19	20	27
Income before income tax expense	295	250	847	704
Income tax expense	94	88	279	245
NET INCOME	201	162	568	459
Total average assets	49,833	47,902	49,604	46,869
Other Non-Segment
Segment Reporting Information [Line Items]
Net interest income	34	(3)	80	27
Noninterest income	18	83	54	120
Total revenue	52	80	134	147
Noninterest expense	15	36	60	53
Profit before provision for credit losses	37	44	74	94
Provision for credit losses	7	10	29	71
Income before income tax expense	30	34	45	23
Income tax expense	5	(9)	(38)	(28)
NET INCOME	25	43	83	51
Total average assets	$ 40,167	$ 39,808	$ 40,649	$ 39,101