GOODWILL AND INTANGIBLE ASSETS - Goodwill Rollforward (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Goodwill [Roll Forward]
Balance at beginning of period	$ 6,887
Business acquisition	59
Balance at end of period	6,946
Consumer Banking
Goodwill [Roll Forward]
Balance at beginning of period	2,136
Business acquisition	59
Balance at end of period	2,195
Commercial Banking
Goodwill [Roll Forward]
Balance at beginning of period	4,751
Business acquisition	0
Balance at end of period	$ 4,751