BENEFITS PAYABLE - Reconciliation to Consolidated (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	$ 4,884
Reinsurance recoverable on unpaid claims	77	$ 70	$ 71	$ 76
Benefits payable	4,961	4,668	4,761	4,563
Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Reinsurance recoverable on unpaid claims	77	70	71	76
Benefits payable	4,321	3,963	3,967	3,507
Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable	576	568	547	578
Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable	28	$ 101	$ 221	$ 454
Operating Segments | Retail
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	4,244
Operating Segments | Group and Specialty
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	576
Operating Segments | Individual Commercial
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	28
Other Businesses
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits payable, net of reinsurance	$ 36