BENEFITS PAYABLE - Reconciliation to Consolidated (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	$ 4,922
Reinsurance recoverable on unpaid claims	98	$ 70	$ 70	$ 76
Benefits payable	5,020	4,668	4,959	4,563
Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Reinsurance recoverable on unpaid claims	98	70	70	76
Benefits payable	4,437	3,963	4,236	3,507
Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable	574	568	561	578
Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable	9	$ 101	$ 134	$ 454
Operating Segments | Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	4,339
Operating Segments | Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	574
Operating Segments | Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	9
Other Businesses
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	$ 0