FAIR VALUE MEASUREMENTS - Narrative (Details) $ in Millions	Dec. 31, 2018 USD ($) hedge_fund	Dec. 31, 2017 USD ($)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Number of hedge funds with reporting lag | hedge_fund	2
Percentage of funds reported on a lag	61.00%	44.00%
Reported Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 1,342	$ 1,341
Other notes payable		36
Estimate of Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior notes	$ 1,334	1,412
Other notes payable		$ 36