DERIVATIVE FINANCIAL INSTRUMENTS - Nature and Accounting Treatment of Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Other long-term investments, Fair Value	$ 1,407,774	$ 995,493
Derivatives with PLC
Derivative [Line Items]
Other long-term investments, Fair Value	133,486	115,379
Embedded derivative - Modco reinsurance treaties
Derivative [Line Items]
Other long-term investments, Fair Value	83,379	31,926
Embedded derivative - GLWB
Derivative [Line Items]
Other long-term investments, Fair Value	48,091	62,538
Derivatives not designated as hedging instruments
Derivative [Line Items]
Other long-term investments, Notional Amounts	15,630,314	15,570,523
Other long-term investments, Fair Value	1,407,774	995,493
Other liabilities. Notional Amount	22,234,390	17,356,887
Other liabilities, Fair Value	2,403,594	1,547,178
Derivatives not designated as hedging instruments | Interest rate swaps
Derivative [Line Items]
Other long-term investments, Notional Amounts	1,628,000	2,228,000
Other long-term investments, Fair Value	210,420	98,655
Other liabilities. Notional Amount	1,194,000	50,000
Other liabilities, Fair Value	0	0
Derivatives not designated as hedging instruments | Total return swaps
Derivative [Line Items]
Other long-term investments, Notional Amounts	433,231	269,772
Other long-term investments, Fair Value	7,018	941
Other liabilities. Notional Amount	418,088	579,675
Other liabilities, Fair Value	7,112	3,229
Derivatives not designated as hedging instruments | Derivatives with PLC
Derivative [Line Items]
Other long-term investments, Notional Amounts	2,618,962	2,830,889
Other long-term investments, Fair Value	133,486	115,379
Derivatives not designated as hedging instruments | Embedded derivative - Modco reinsurance treaties
Derivative [Line Items]
Other long-term investments, Notional Amounts	1,269,954	1,280,189
Other long-term investments, Fair Value	83,379	31,926
Other liabilities. Notional Amount	2,892,930	2,263,685
Other liabilities, Fair Value	331,836	231,516
Derivatives not designated as hedging instruments | Funds withheld derivative
Derivative [Line Items]
Other liabilities. Notional Amount	3,810,657	1,845,649
Other liabilities, Fair Value	145,030	70,583
Derivatives not designated as hedging instruments | Embedded derivative - GLWB
Derivative [Line Items]
Other long-term investments, Notional Amounts	610,426	1,147,436
Other long-term investments, Fair Value	48,091	62,538
Other liabilities. Notional Amount	3,359,799	2,892,926
Other liabilities, Fair Value	566,337	248,577
Derivatives not designated as hedging instruments | Embedded derivative - FIA
Derivative [Line Items]
Other long-term investments, Notional Amounts	310,468	0
Other long-term investments, Fair Value	55,038	0
Other liabilities. Notional Amount	3,656,227	2,892,803
Other liabilities, Fair Value	580,268	332,869
Derivatives not designated as hedging instruments | Embedded derivative - IUL
Derivative [Line Items]
Other liabilities. Notional Amount	339,564	301,598
Other liabilities, Fair Value	194,228	151,765
Derivatives not designated as hedging instruments | Interest rate futures
Derivative [Line Items]
Other long-term investments, Notional Amounts	700,637	896,073
Other long-term investments, Fair Value	4,818	7,557
Other liabilities. Notional Amount	421,631	669,223
Other liabilities, Fair Value	1,825	10,375
Derivatives not designated as hedging instruments | Equity futures
Derivative [Line Items]
Other long-term investments, Notional Amounts	156,317	159,901
Other long-term investments, Fair Value	2,063	2,109
Other liabilities. Notional Amount	162,260	174,743
Other liabilities, Fair Value	3,571	2,376
Derivatives not designated as hedging instruments | Currency futures
Derivative [Line Items]
Other long-term investments, Notional Amounts	161,793	72,593
Other long-term investments, Fair Value	1,750	131
Other liabilities. Notional Amount	128,613	192,306
Other liabilities, Fair Value	1,016	1,836
Derivatives not designated as hedging instruments | Equity options
Derivative [Line Items]
Other long-term investments, Notional Amounts	7,740,526	6,685,670
Other long-term investments, Fair Value	861,711	676,257
Other liabilities. Notional Amount	5,465,007	4,827,714
Other liabilities, Fair Value	507,408	429,434
Derivatives not designated as hedging instruments | Other
Derivative [Line Items]
Other liabilities. Notional Amount	268,436	199,387
Other liabilities, Fair Value	46,236	53,245
Derivatives designated as hedging instrument | Cash flow hedges | Interest rate swaps
Derivative [Line Items]
Other liabilities. Notional Amount	0	350,000
Other liabilities, Fair Value	0	0
Derivatives designated as hedging instrument | Cash flow hedges | Foreign currency swaps
Derivative [Line Items]
Other liabilities. Notional Amount	117,178	117,178
Other liabilities, Fair Value	$ 18,727	$ 11,373