BENEFITS PAYABLE - Activity in Benefits Payable (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance	$ 4,563	$ 4,976
Less: Premium deficiency reserve	0	(176)
Less: Reinsurance recoverables	(76)	(85)
Balance	4,487	4,715
Incurred related to:
Current year	33,318	34,340
Prior years	(430)	(525)
Total incurred	32,888	33,815
Paid related to:
Current year	(28,741)	(29,768)
Prior years	(3,745)	(3,996)
Total paid	(32,486)	(33,764)
Premium deficiency reserve	0	206
Reinsurance recoverable	70	77
Ending balance	4,959	5,049
Retail
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance	3,507	3,600
Less: Reinsurance recoverables	(76)	(85)
Balance	3,431	3,515
Incurred related to:
Current year	29,356	28,369
Prior years	(339)	(378)
Total incurred	29,017	27,991
Paid related to:
Current year	(25,460)	(24,822)
Prior years	(2,822)	(2,990)
Total paid	(28,282)	(27,812)
Reinsurance recoverable	70	77
Ending balance	4,236	3,771
Total IBNR	2,700
Group and Specialty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance	578	616
Incurred related to:
Current year	3,996	3,918
Prior years	(44)	(42)
Total incurred	3,952	3,876
Paid related to:
Current year	(3,452)	(3,337)
Prior years	(517)	(557)
Total paid	(3,969)	(3,894)
Ending balance	561	598
Total IBNR	490
Individual Commercial
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance	454	740
Less: Premium deficiency reserve	0	(176)
Balance	454	564
Incurred related to:
Current year	502	2,694
Prior years	(46)	(104)
Total incurred	456	2,590
Paid related to:
Current year	(393)	(2,273)
Prior years	(383)	(430)
Total paid	(776)	(2,703)
Premium deficiency reserve	0	206
Ending balance	134	$ 657
Total IBNR	$ 120