HEALTH CARE REFORM (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 02, 2017
Supplementary Insurance Information, by Segment [Line Items]
Premium deficiency reserve				$ 176
Change in full year estimate recorded in benefits expense		$ 208
Current period results applied to the PDR liability for the 2016 coverage year				(384)
Premiums reduction, write off of risk corridor receivables	$ 583
Litigation Recoveries Sought						$ 611
Other current assets	3,438		$ 2,949	3,438
Trade accounts payable and accrued expenses	(2,467)		(4,069)	(2,467)
Other long-term assets	2,226		2,166	2,226
Proceeds from risk corridor settlements				383
Individual Commercial
Supplementary Insurance Information, by Segment [Line Items]
Premium deficiency reserve				176
Risk Adjustment Settlement
Supplementary Insurance Information, by Segment [Line Items]
Total net (liability) asset	196		(13)	196
Reinsurance Recoverables
Supplementary Insurance Information, by Segment [Line Items]
Total net (liability) asset	260		44	260
Risk Corridor Settlement
Supplementary Insurance Information, by Segment [Line Items]
Total net (liability) asset	0		0	0
2014 and 2015 Coverage Years
Supplementary Insurance Information, by Segment [Line Items]
Premiums reduction, write off of risk corridor receivables	415
2014 Coverage Year
Supplementary Insurance Information, by Segment [Line Items]
Decrease in premiums receivable			39
Prior Coverage Years
Supplementary Insurance Information, by Segment [Line Items]
Proceeds from risk corridor settlements			440
Prior Coverage Years | Risk Adjustment Settlement
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	307		0	307
Other current assets	0		0	0
Trade accounts payable and accrued expenses	(117)		0	(117)
Net current (liability) asset	190		0	190
Other long-term assets	6		0	6
Total net (liability) asset	196		0	196
Prior Coverage Years | Reinsurance Recoverables
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	0		0	0
Other current assets	260		44	260
Trade accounts payable and accrued expenses	0		0	0
Net current (liability) asset	260		44	260
Other long-term assets	0		0	0
Total net (liability) asset	260		44	260
Prior Coverage Years | Risk Corridor Settlement
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	0		0	0
Other current assets	0		0	0
Trade accounts payable and accrued expenses	0		0	0
Net current (liability) asset	0		0	0
Other long-term assets	0		0	0
Total net (liability) asset	0		0	0
Current Coverage Year | Risk Adjustment Settlement
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	0		62	0
Trade accounts payable and accrued expenses	0		(80)	0
Net current (liability) asset	0		(18)	0
Other long-term assets	0		5	0
Total net (liability) asset	0		(13)	0
Current Coverage Year | Reinsurance Recoverables
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	0		0	0
Trade accounts payable and accrued expenses	0		0	0
Net current (liability) asset	0		0	0
Other long-term assets	0		0	0
Total net (liability) asset	0		0	0
Current Coverage Year | Risk Corridor Settlement
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	0		0	0
Trade accounts payable and accrued expenses	0		0	0
Net current (liability) asset	0		0	0
Other long-term assets	0		0	0
Total net (liability) asset	$ 0		$ 0	0
Health Care Reform
Supplementary Insurance Information, by Segment [Line Items]
Payment of annual health insurance industry fee				$ 916	$ 867