DERIVATIVE FINANCIAL INSTRUMENTS - Nature and Accounting Treatment of Derivative Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	$ 16,161,834	$ 15,570,523
Derivative asset, fair value	1,559,405	995,493
Derivative liability, notional amount	22,126,153	17,356,887
Derivative liability, fair value	2,681,451	1,547,178
Interest rate swaps | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	1,478,000	2,228,000
Derivative asset, fair value	184,943	98,655
Derivative liability, notional amount	1,354,000	50,000
Derivative liability, fair value	0	0
Total return swaps | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	158,181	269,772
Derivative asset, fair value	2,294	941
Derivative liability, notional amount	1,002,691	579,675
Derivative liability, fair value	14,986	3,229
Derivatives with PLC
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, fair value	0	115,379
Derivatives with PLC | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	4,076,499	2,830,889
Derivative asset, fair value	0	115,379
Embedded derivative - Modco reinsurance treaties
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, fair value	100,505	31,926
Derivative liability, fair value	388,521	231,516
Embedded derivative - Modco reinsurance treaties | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	1,248,887	1,280,189
Derivative asset, fair value	100,505	31,926
Derivative liability, notional amount	2,910,662	2,263,685
Derivative liability, fair value	388,521	231,516
Funds withheld derivative
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, fair value	66,331	70,583
Funds withheld derivative | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, notional amount	2,427,320	1,845,649
Derivative liability, fair value	66,331	70,583
Embedded derivative - GLWB
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, fair value	61,356	62,538
Derivative liability, fair value	465,012	248,577
Embedded derivative - GLWB | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	763,917	1,147,436
Derivative asset, fair value	61,356	62,538
Derivative liability, notional amount	3,397,244	2,892,926
Derivative liability, fair value	465,012	248,577
Embedded derivative - FIA
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, fair value	633,350	332,869
Embedded derivative - FIA | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	335,000	0
Derivative asset, fair value	60,134	0
Derivative liability, notional amount	3,888,985	2,892,803
Derivative liability, fair value	633,350	332,869
Embedded derivative - IUL
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, fair value	201,331	151,765
Embedded derivative - IUL | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, notional amount	356,641	301,598
Derivative liability, fair value	201,331	151,765
Interest rate futures | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	690,398	896,073
Derivative asset, fair value	4,170	7,557
Derivative liability, notional amount	414,874	669,223
Derivative liability, fair value	3,389	10,375
Equity futures | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	202,839	159,901
Derivative asset, fair value	4,189	2,109
Derivative liability, notional amount	189,808	174,743
Derivative liability, fair value	4,713	2,376
Currency futures | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	0	72,593
Derivative asset, fair value	0	131
Derivative liability, notional amount	264,367	192,306
Derivative liability, fair value	3,612	1,836
Equity options | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative asset, notional a mount	7,208,113	6,685,670
Derivative asset, fair value	1,141,814	676,257
Derivative liability, notional amount	5,498,929	4,827,714
Derivative liability, fair value	834,407	429,434
Other | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, notional amount	303,454	199,387
Derivative liability, fair value	55,613	53,245
Cash flow hedges | Interest rate swaps | Cash flow hedges
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, notional amount	0	350,000
Derivative liability, fair value	0	0
Cash flow hedges | Foreign currency swaps | Cash flow hedges
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability, notional amount	117,178	117,178
Derivative liability, fair value	$ 10,186	$ 11,373