EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator (basic and diluted):
Net income	$ 1,652	$ 1,045	$ 840
Less: Preferred stock dividends	14	14	7
Net income available to common stockholders	$ 1,638	$ 1,031	$ 833
Denominator:
Weighted-average common shares outstanding - basic (in shares)	502,157,440	522,093,545	535,599,731
Dilutive common shares: share-based awards (in shares)	1,527,651	1,837,173	2,621,167
Weighted-average common shares outstanding - diluted (in shares)	503,685,091	523,930,718	538,220,898
Earnings per common share:
Basic (in dollars per share)	$ 3.26	$ 1.97	$ 1.55
Diluted (in dollars per share)	$ 3.25	$ 1.97	$ 1.55
Antidilutive securities (in shares)	533	0	0