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	$ 41,900,618	$ 30,956,792
Unearned premiums	769,620	751,130
Total policy liabilities and accruals	42,670,238	31,707,922
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Future policy benefits	4,213,399	4,526,075
Unearned premiums	272,630	274,816
Total policy liabilities and accruals and associated reinsurance receivable	4,486,029	4,800,891
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	3,573,500	3,885,546
Future policy benefits	3,957,120	4,248,379
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	383,620	362,833
Other Insurance
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Benefit reserves	142,855	157,101
Unpaid claim liabilities	220,457	231,565
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Benefit reserves	80,688	92,330
Unpaid claim liabilities	$ 175,591	$ 185,366