BENEFITS PAYABLE - Reconciliation to Consolidated (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	$ 5,770
Reinsurance recoverable on unpaid claims	72	$ 95	$ 86	$ 70
Benefits payable	5,842	4,862	5,020	4,668
Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Reinsurance recoverable on unpaid claims	72	95	86	70
Benefits payable	5,243	4,338	4,413	3,963
Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable	599	$ 517	$ 609	$ 568
Operating Segments | Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	5,171
Reinsurance recoverable on unpaid claims	72
Operating Segments | Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	$ 599