SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Future Policy Benefit Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Future policy benefits	$ 4,539,062	$ 4,819,876
Unearned premiums	536,636	503,970
Total policy liabilities and accruals and associated reinsurance receivable	5,075,698	5,323,846
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Future policy benefits	30,957,592	30,511,085
Unearned premiums	875,405	848,495
Total policy liabilities and accruals	31,832,997	31,359,580
Life and Annuity Insurance
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Benefit reserves	3,898,079	4,191,845
Future policy benefits	4,260,906	4,515,475
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Benefit reserves	29,972,938	29,574,479
Future policy benefits	30,568,126	30,091,736
Life insurance
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Unpaid claim liabilities	362,827	323,630
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Unpaid claim liabilities	595,188	517,257
Other Insurance
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Benefit reserves	92,330	103,746
Unpaid claim liabilities	185,826	200,655
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Benefit reserves	157,101	170,519
Unpaid claim liabilities	$ 232,365	$ 248,830