ACCOUNTS RECEIVABLE AND OTHER FINANCIAL ASSETS - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables from customers, gross, current	$ 510	$ 1,200
Receivables from marketing affiliates, gross, current	32	110
Accounts receivable, credit loss expense	216	69	$ 79
Prepaid expenses, allowance for credit loss	55	6
Prepaid expenses, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Prepayments to certain customers	107	232
Other assets, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Prepayments to certain customers	45
Sales and other expenses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for other credit losses	230	$ 69
Sales and other expenses | Prepayments to customers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for other credit losses	51
Merchant revenue
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, credit loss expense	$ 37