INVESTMENT OPERATIONS - Schedule of Available-for-Sale Credit Losses on Fixed Maturities With Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Additions for securities for which allowance was not previously recorded	$ 38,459	$ 120,540
Ending Balance	19,399	19,399
Corporate securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning Balance	81,426	0
Additions for securities for which allowance was not previously recorded	0	62,442
Adjustments on previously recorded allowances due to change in expected cash flows	945	19,929
Reductions on previously recorded allowances due to disposal of security in the current period	0	0
Write-offs of previously recorded allowances due to intent or requirement to sell	(63,617)	(63,617)
Ending Balance	18,754	18,754
Other asset-backed securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning Balance	655	0
Additions for securities for which allowance was not previously recorded	0	658
Adjustments on previously recorded allowances due to change in expected cash flows	0	0
Reductions on previously recorded allowances due to disposal of security in the current period	(10)	(13)
Write-offs of previously recorded allowances due to intent or requirement to sell	0	0
Ending Balance	645	645
Fixed maturities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning Balance	82,081	0
Additions for securities for which allowance was not previously recorded	0	63,100
Adjustments on previously recorded allowances due to change in expected cash flows	945	19,929
Reductions on previously recorded allowances due to disposal of security in the current period	(10)	(13)
Write-offs of previously recorded allowances due to intent or requirement to sell	(63,617)	(63,617)
Ending Balance	$ 19,399	$ 19,399