SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Future Policy Benefit Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Future policy benefits	$ 41,901,552	$ 30,957,592
Unearned premiums	872,594	875,405
Total policy liabilities and accruals	42,774,146	31,832,997
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Future policy benefits	4,223,069	4,539,062
Unearned premiums	541,674	536,636
Total policy liabilities and accruals and associated reinsurance receivable	4,764,743	5,075,698
Life and Annuity Insurance
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Benefit reserves	40,883,229	29,972,938
Future policy benefits	41,537,306	30,568,126
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Benefit reserves	3,582,850	3,898,079
Future policy benefits	3,966,226	4,260,906
Life insurance
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Unpaid claim liabilities	654,077	595,188
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Unpaid claim liabilities	383,376	362,827
Other Insurance
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Benefit reserves	142,855	157,101
Unpaid claim liabilities	221,391	232,365
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Benefit reserves	80,688	92,330
Unpaid claim liabilities	$ 176,155	$ 185,826