BENEFITS PAYABLE - Activity in Benefits Payable (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 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	45,693	40,499
Prior years	(278)	(331)
Total incurred	45,415	40,168
Paid related to:
Current year	(37,810)	(34,625)
Prior years	(5,334)	(4,158)
Total paid	(43,144)	(38,783)
Reinsurance recoverable	1	68
Balances, end of period	8,208	6,220
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	42,186	36,762
Prior years	(235)	(366)
Total incurred	41,951	36,396
Paid related to:
Current year	(34,946)	(31,476)
Prior years	(4,759)	(3,634)
Total paid	(39,705)	(35,110)
Reinsurance recoverable	1	68
Balances, end of period	7,542	5,597
Total IBNR included in benefits payable	4,600
Group and Specialty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	641	517
Incurred related to:
Current year	3,929	4,142
Prior years	(43)	35
Total incurred	3,886	4,177
Paid related to:
Current year	(3,286)	(3,547)
Prior years	(575)	(524)
Total paid	(3,861)	(4,071)
Balances, end of period	666	$ 623
Total IBNR included in benefits payable	$ 576