SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Future Minimum Lease Payments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Operating Leases
2019	$ 159
2020	111
2021	46
2022	40
2023	24
Thereafter	41
Total future minimum lease payments	421
Less: imputed interest	(34)
Total lease liabilities	387
Current portion	(187)
Non-current portion	200
Finance Leases
2019	22
2020	13
2021	3
2022	3
2023	3
Thereafter	39
Total future minimum lease payments	83
Less: imputed interest	(15)
Total lease liabilities	68	$ 1
Current portion	(30)
Non-current portion	$ 38