BENEFITS PAYABLE - Activity in Benefits Payable (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	$ 8,143	$ 6,004
Less: Reinsurance recoverables	0	(68)
Balances, beginning of period, net	8,143	5,936
Acquisitions	42	0
Incurred related to:
Current year	35,164	30,039
Prior years	(719)	(235)
Total incurred	34,445	29,804
Paid related to:
Current year	(27,556)	(22,665)
Prior years	(6,589)	(5,098)
Total paid	(34,145)	(27,763)
Reinsurance recoverable	0	3
Balances, end of period	8,485	7,980
Retail
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	7,428	5,363
Less: Reinsurance recoverables	0	(68)
Balances, beginning of period, net	7,428	5,295
Acquisitions	42	0
Incurred related to:
Current year	32,986	27,921
Prior years	(619)	(205)
Total incurred	32,367	27,716
Paid related to:
Current year	(25,953)	(21,063)
Prior years	(5,990)	(4,528)
Total paid	(31,943)	(25,591)
Reinsurance recoverable	0	3
Balances, end of period	7,894	7,423
Total IBNR included in benefits payable	4,900
Group and Specialty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	715	641
Incurred related to:
Current year	2,492	2,434
Prior years	(100)	(30)
Total incurred	2,392	2,404
Paid related to:
Current year	(1,917)	(1,918)
Prior years	(599)	(570)
Total paid	(2,516)	(2,488)
Balances, end of period	591	$ 557
Total IBNR included in benefits payable	$ 514