BENEFITS PAYABLE - Activity in Benefits Payable (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	$ 6,004	$ 4,862
Less: Reinsurance recoverables	(68)	(95)
Balances, beginning of period, net	5,936	4,767
Incurred related to:
Current year	30,039	27,086
Prior years	(235)	(275)
Total incurred	29,804	26,811
Paid related to:
Current year	(22,665)	(21,700)
Prior years	(5,098)	(4,108)
Total paid	(27,763)	(25,808)
Reinsurance recoverable	3	72
Balances, end of period	7,980	5,842
Retail
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	5,363	4,338
Less: Reinsurance recoverables	(68)	(95)
Balances, beginning of period, net	5,295	4,243
Incurred related to:
Current year	27,921	24,657
Prior years	(205)	(311)
Total incurred	27,716	24,346
Paid related to:
Current year	(21,063)	(19,826)
Prior years	(4,528)	(3,592)
Total paid	(25,591)	(23,418)
Reinsurance recoverable	3	72
Balances, end of period	7,423	5,243
Total IBNR included in benefits payable	4,400
Group and Specialty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	641	517
Incurred related to:
Current year	2,434	2,693
Prior years	(30)	36
Total incurred	2,404	2,729
Paid related to:
Current year	(1,918)	(2,131)
Prior years	(570)	(516)
Total paid	(2,488)	(2,647)
Balances, end of period	557	$ 599
Total IBNR included in benefits payable	$ 490