SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Future Policy Benefit Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Future policy benefits	$ 53,943,962	$ 41,900,618
Unearned premiums	794,832	769,620
Total policy liabilities and accruals	54,738,794	42,670,238
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Future policy benefits	3,893,235	4,213,399
Unearned premiums	287,865	272,630
Total policy liabilities and accruals and associated reinsurance receivable	4,181,100	4,486,029
Life and Annuity Insurance
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Benefit reserves	52,478,019	40,883,229
Future policy benefits	53,288,604	41,537,306
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Benefit reserves	3,279,374	3,573,500
Future policy benefits	3,653,316	3,957,120
Life insurance
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Unpaid claim liabilities	810,585	654,077
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Unpaid claim liabilities	373,942	383,620
Other Insurance
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Benefit reserves	422,579	142,855
Unpaid claim liabilities	232,779	220,457
Reinsurance Recoverables, Including Reinsurance Premium Paid [Abstract]
Benefit reserves	69,316	80,688
Unpaid claim liabilities	$ 170,603	$ 175,591