BENEFITS PAYABLE - Benefits Expense (Details) claim in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) claim	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	$ (582)	$ (236)	$ (518)
Benefits payable, net of reinsurance	4,487	4,715	4,397	$ 3,893
Reinsurance recoverable on unpaid claims	76	85	78	0
Benefits payable	4,563	4,976	4,475	3,893
Favorable Medical Claims Reserve Development	582	236	518
Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(535)	(228)	(488)
Incurred Claims, Net of Reinsurance	113,892
Total IBNR	2,900
Cumulative Paid Claims, Net of Reinsurance	109,992
Liabilities for claims and claim adjustment expenses, net of reinsurance	3,900
Benefits payable, net of reinsurance		4,035	3,801	3,268
Reinsurance recoverable on unpaid claims	76	85	78	0
Benefits payable	3,976	4,296	3,879	3,268
Retail | 2014 Coverage Year
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	$ 33,749	33,800	33,996
Cumulative Number of Reported Claims - Service Date | claim	74.3
Cumulative Paid Claims, Net of Reinsurance	$ 33,740	33,704	30,305
Retail | Prior Coverage Years
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	$ 39,289	39,760
Cumulative Number of Reported Claims - Service Date | claim	88.8
Cumulative Paid Claims, Net of Reinsurance	$ 39,285	35,835
Retail | Current Coverage Year
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	$ 40,854
Cumulative Number of Reported Claims - Service Date | claim	87.7
Cumulative Paid Claims, Net of Reinsurance	$ 36,967
Group
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(46)	(7)	(29)
Incurred Claims, Net of Reinsurance	15,512
Total IBNR	468
Cumulative Paid Claims, Net of Reinsurance	14,949
Liabilities for claims and claim adjustment expenses, net of reinsurance	563
Benefits payable, net of reinsurance		600	578	577
Reinsurance recoverable on unpaid claims	0	0	0	0
Benefits payable	563	600	578	$ 577
Group | 2014 Coverage Year
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	$ 5,135	5,135	5,148
Cumulative Number of Reported Claims - Service Date | claim	27.3
Cumulative Paid Claims, Net of Reinsurance	$ 5,134	5,126	4,574
Group | Prior Coverage Years
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	$ 5,217	5,261
Cumulative Number of Reported Claims - Service Date | claim	29.1
Cumulative Paid Claims, Net of Reinsurance	$ 5,210	4,671
Group | Current Coverage Year
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	$ 5,160
Cumulative Number of Reported Claims - Service Date | claim	23.3
Cumulative Paid Claims, Net of Reinsurance	$ 4,605
Other insurance lines
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(1)	$ (1)	$ (1)
Benefits payable, net of reinsurance	24
Reinsurance recoverable on unpaid claims	$ 0