BENEFITS PAYABLE - Activity in Benefits Payable (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
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	11,580	11,751
Prior years	(231)	(340)
Total incurred	11,349	11,411
Paid related to:
Current year	(7,695)	(7,692)
Prior years	(3,451)	(3,576)
Total paid	(11,146)	(11,268)
Premium deficiency reserve	0	(189)
Reinsurance recoverable	(71)	(67)
Ending balance	4,761	5,114
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	10,255	9,851
Prior years	(204)	(218)
Total incurred	10,051	9,633
Paid related to:
Current year	(7,014)	(6,706)
Prior years	(2,572)	(2,685)
Total paid	(9,586)	(9,391)
Reinsurance recoverable	(71)	(67)
Ending balance	3,967	3,824
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	1,306	1,260
Prior years	(20)	(41)
Total incurred	1,286	1,219
Paid related to:
Current year	(824)	(728)
Prior years	(493)	(502)
Total paid	(1,317)	(1,230)
Ending balance	547	605
Total IBNR	468
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	185	826
Prior years	(6)	(80)
Total incurred	179	746
Paid related to:
Current year	(49)	(465)
Prior years	(363)	(370)
Total paid	(412)	(835)
Premium deficiency reserve	0	(189)
Ending balance	221	$ 664
Total IBNR	$ 169