BENEFITS PAYABLE - Reconciliation to Consolidated (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	$ 4,992
Reinsurance recoverable on unpaid claims	86	$ 70	$ 78	$ 76
Benefits payable	5,020	4,668	4,838	4,563
Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Reinsurance recoverable on unpaid claims	86	70	78	76
Benefits payable	4,413	3,963	4,140	3,507
Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable	609	568	541	578
Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable	15	$ 101	131	$ 454
Operating Segments | Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	4,327
Operating Segments | Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	609
Operating Segments | Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	15
Other Businesses
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	41
Disposal Group, Held-for-sale, Not Discontinued Operations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Held-for-sale	$ (58)		$ 0