BASIS OF PRESENTATION AND SIGNIFICANT EVENTS - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Oct. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Receivables and Other [Line Items]
Accounts receivable				$ 848	$ 1,015
Health Care Reform
Receivables and Other [Line Items]
Payment of annual health insurance industry fee	$ 1,040
Amortization of deferred charges		$ 258	$ 778
Services Accounts Receivable
Receivables and Other [Line Items]
Accounts receivable				$ 141