BASIS OF PRESENTATION AND SIGNIFICANT EVENTS - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Receivables and Other [Line Items]
Contributions to Humana Foundation to promote COVID-19 relief efforts		$ 50
Accounts receivable		2,009	$ 1,056
Amortization of deferred costs		306
Forecast | Health Care Reform
Receivables and Other [Line Items]
Payment of annual health insurance industry fee	$ 1,200
Services Accounts Receivable
Receivables and Other [Line Items]
Accounts receivable		$ 141