INCOME TAXES - COMPONENTS OF TAX EXPENSE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax expense (benefit):
Federal	$ 127	$ 392	$ 397
State	35	48	30
Total current	162	440	427
Deferred tax expense:
Federal	(30)	77	60
State	41	14	(23)
Total deferred	11	91	37
Income tax expense	$ 173	$ 531	$ 464