BENEFITS PAYABLE - Activity in Benefits Payable (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	$ 4,862	$ 4,668
Less: Reinsurance recoverables	(95)	(70)
Balances, beginning of period, net	4,767	4,598
Incurred related to:
Current year	27,086	23,543
Prior years	(275)	(338)
Total incurred	26,811	23,205
Paid related to:
Current year	(21,700)	(18,914)
Prior years	(4,108)	(3,897)
Total paid	(25,808)	(22,811)
Reinsurance recoverable	72	86
Less: Held-for-sale	0	(58)
Balances, end of period	5,842	5,020
Retail
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	4,338	3,963
Less: Reinsurance recoverables	(95)	(70)
Balances, beginning of period, net	4,243	3,893
Incurred related to:
Current year	24,657	21,069
Prior years	(311)	(247)
Total incurred	24,346	20,822
Paid related to:
Current year	(19,826)	(17,061)
Prior years	(3,592)	(3,327)
Total paid	(23,418)	(20,388)
Reinsurance recoverable	72	86
Balances, end of period	5,243	4,413
Total IBNR	3,200
Group and Specialty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	517	568
Incurred related to:
Current year	2,693	2,665
Prior years	36	(34)
Total incurred	2,729	2,631
Paid related to:
Current year	(2,131)	(2,094)
Prior years	(516)	(496)
Total paid	(2,647)	(2,590)
Balances, end of period	599	609
Total IBNR	$ 505
Individual Commercial
Incurred related to:
Total incurred		$ 55