SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CASH EQUIVALENTS AND RESTRICTED CASH EQUIVALENTS (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 2,008	$ 3,032
Restricted cash and restricted cash equivalents	170	485
Cash and restricted cash included in assets held for sale	0	3
Restricted cash and restricted cash equivalents included in long-term receivables and other assets, net	16	54
Cash, cash equivalents, restricted cash and restricted cash equivalents	$ 2,194	$ 3,574	$ 3,033	$ 1,672