INCOME TAXES - EFFECTIVE INCOME TAX RECONCILIATION (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
U.S. federal tax rate		35.00%	35.00%	35.00%
Income before income tax			$ 975	$ 816
Income (loss) before income tax		$ 1,312	975	816
Expected tax expense		459	341	286
Nondeductible expenses		4	4	4
State income taxes		19	25	21
State income sourcing		(15)	0	0
Other—net		(3)	0	(3)
Total tax expense related to income		$ 464	$ 370	$ 308
Effective tax rate		35.40%	37.90%	37.70%
Tax amendment, cumulative benefit	$ 26
Additions based on tax positions and settlements related to the current year	$ 18	$ 19	$ 1	$ 1