BENEFITS PAYABLE - Activity in Benefits Payable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	$ 4,862	$ 4,668	$ 4,563
Less: Reinsurance recoverables	(95)	(70)	(76)
Balances, beginning of period, net	4,767	4,598	4,487
Incurred related to:
Current year	54,193	46,385	44,001
Prior years	(336)	(503)	(483)
Total incurred	53,857	45,882	43,518
Paid related to:
Current year	(48,421)	(41,736)	(39,496)
Prior years	(4,267)	(3,977)	(3,911)
Total paid	(52,688)	(45,713)	(43,407)
Reinsurance recoverable	68	95	70
Balances, end of period	6,004	4,862	4,668
Retail
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	4,338	3,963	3,506
Less: Reinsurance recoverables	(95)	(70)	(76)
Balances, beginning of period, net	4,243	3,893	3,430
Incurred related to:
Current year	48,983	41,323	38,604
Prior years	(386)	(398)	(386)
Total incurred	48,597	40,925	38,218
Paid related to:
Current year	(43,831)	(37,189)	(34,781)
Prior years	(3,714)	(3,386)	(2,974)
Total paid	(47,545)	(40,575)	(37,755)
Reinsurance recoverable	68	95	70
Balances, end of period	5,363	4,338	3,963
Group and Specialty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balances, beginning of period	517	568	579
Incurred related to:
Current year	5,708	5,466	5,403
Prior years	50	(46)	(40)
Total incurred	5,758	5,420	5,363
Paid related to:
Current year	(5,081)	(4,957)	(4,843)
Prior years	(553)	(514)	(531)
Total paid	(5,634)	(5,471)	(5,374)
Balances, end of period	$ 641	$ 517	$ 568