BENEFITS PAYABLE - Activity in Benefits Payable (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	$ 8,289	$ 8,143
Acquisitions	0	42
Incurred related to:
Current year	19,985	17,851
Prior years	(360)	(555)
Total incurred	19,625	17,296
Paid related to:
Current year	(12,284)	(10,842)
Prior years	(6,252)	(5,988)
Total paid	(18,536)	(16,830)
Balances, end of period	9,378	8,651
Retail
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	7,675	7,428
Acquisitions	0	42
Incurred related to:
Current year	19,078	16,762
Prior years	(328)	(463)
Total incurred	18,750	16,299
Paid related to:
Current year	(11,882)	(10,330)
Prior years	(5,741)	(5,401)
Total paid	(17,623)	(15,731)
Balances, end of period	8,802	8,038
Total IBNR included in benefits payable	5,300
Group and Specialty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	614	715
Incurred related to:
Current year	1,078	1,237
Prior years	(32)	(92)
Total incurred	1,046	1,145
Paid related to:
Current year	(573)	(660)
Prior years	(511)	(587)
Total paid	(1,084)	(1,247)
Balances, end of period	576	$ 613
Total IBNR included in benefits payable	$ 492