BENEFITS PAYABLE - Benefits Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	$ (483)	$ (582)	$ (236)
Benefits payable, net of reinsurance	4,598
Reinsurance recoverable on unpaid claims	70	76	85	$ 78
Total benefits payable, gross	4,668	4,563	4,976	4,475
Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(386)	(429)	(248)
Incurred Claims, Net of Reinsurance	111,372
Cumulative Paid Claims, Net of Reinsurance	107,479
Reinsurance recoverable on unpaid claims	70	76	85	78
Total benefits payable, gross	3,963	3,506	3,600	3,428
Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(40)	(46)	(7)
Incurred Claims, Net of Reinsurance	15,970
Cumulative Paid Claims, Net of Reinsurance	15,402
Reinsurance recoverable on unpaid claims		0	0	0
Total benefits payable, gross	568	579	616	603
Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(56)	(106)	20
Incurred Claims, Net of Reinsurance	7,702
Cumulative Paid Claims, Net of Reinsurance	7,601
Total benefits payable, gross	101	454	741	$ 424
Operating Segments | Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(386)	(429)	(248)
Benefits payable, net of reinsurance	3,893
Reinsurance recoverable on unpaid claims	70
Operating Segments | Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(40)	(46)	(7)
Benefits payable, net of reinsurance	568
Reinsurance recoverable on unpaid claims	0
Operating Segments | Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior years, Incurred	(56)	(106)	20
Benefits payable, net of reinsurance	101
Reinsurance recoverable on unpaid claims	0
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	36
Reinsurance recoverable on unpaid claims	0
2015 Claims Incurred Year | Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	35,877	35,928	36,299
Cumulative Paid Claims, Net of Reinsurance	35,857	35,918	32,874
2015 Claims Incurred Year | Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	5,333	5,333	5,377
Cumulative Paid Claims, Net of Reinsurance	5,333	5,327	4,774
2015 Claims Incurred Year | Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	3,412	3,412	3,512
Cumulative Paid Claims, Net of Reinsurance	3,412	3,400	$ 2,966
2016 Claims Incurred Year | Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	36,891	37,212
Cumulative Paid Claims, Net of Reinsurance	36,841	33,784
2016 Claims Incurred Year | Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	5,234	5,271
Cumulative Paid Claims, Net of Reinsurance	5,226	4,700
2016 Claims Incurred Year | Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	3,621	3,677
Cumulative Paid Claims, Net of Reinsurance	3,606	$ 3,233
2017 Claims Incurred Year | Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	38,604
Cumulative Paid Claims, Net of Reinsurance	34,781
2017 Claims Incurred Year | Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	5,403
Cumulative Paid Claims, Net of Reinsurance	4,843
2017 Claims Incurred Year | Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred Claims, Net of Reinsurance	669
Cumulative Paid Claims, Net of Reinsurance	$ 583