DERIVATIVE FINANCIAL INSTRUMENTS - Nature and Accounting Treatment of Derivative Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Other long-term investments, Fair Value	$ 1,172,964	$ 995,493
Derivatives with PLC
Derivative [Line Items]
Other long-term investments, Fair Value	113,653	115,379
Embedded derivative - Modco reinsurance treaties
Derivative [Line Items]
Other long-term investments, Fair Value	64,758	31,926
Embedded derivative - GLWB
Derivative [Line Items]
Other long-term investments, Fair Value	45,636	62,538
Derivatives not designated as hedging instruments
Derivative [Line Items]
Other long-term investments, Notional Amounts	15,737,291	15,570,523
Other long-term investments, Fair Value	1,172,964	995,493
Other liabilities. Notional Amount	20,441,740	17,356,887
Other liabilities, Fair Value	2,155,762	1,547,178
Derivatives not designated as hedging instruments | Interest rate swaps
Derivative [Line Items]
Other long-term investments, Notional Amounts	2,428,000	2,228,000
Other long-term investments, Fair Value	225,231	98,655
Other liabilities. Notional Amount	250,000	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	562,607	269,772
Other long-term investments, Fair Value	4,460	941
Other liabilities. Notional Amount	194,504	579,675
Other liabilities, Fair Value	2,938	3,229
Derivatives not designated as hedging instruments | Derivatives with PLC
Derivative [Line Items]
Other long-term investments, Notional Amounts	2,653,006	2,830,889
Other long-term investments, Fair Value	113,653	115,379
Derivatives not designated as hedging instruments | Embedded derivative - Modco reinsurance treaties
Derivative [Line Items]
Other long-term investments, Notional Amounts	1,281,470	1,280,189
Other long-term investments, Fair Value	64,758	31,926
Other liabilities. Notional Amount	2,815,598	2,263,685
Other liabilities, Fair Value	289,709	231,516
Derivatives not designated as hedging instruments | Funds withheld derivative
Derivative [Line Items]
Other liabilities. Notional Amount	3,062,874	1,845,649
Other liabilities, Fair Value	159,370	70,583
Derivatives not designated as hedging instruments | Embedded derivative - GLWB
Derivative [Line Items]
Other long-term investments, Notional Amounts	543,139	1,147,436
Other long-term investments, Fair Value	45,636	62,538
Other liabilities. Notional Amount	3,414,058	2,892,926
Other liabilities, Fair Value	636,398	248,577
Derivatives not designated as hedging instruments | Embedded derivative - FIA
Derivative [Line Items]
Other long-term investments, Notional Amounts	286,778	0
Other long-term investments, Fair Value	51,860	0
Other liabilities. Notional Amount	3,256,264	2,892,803
Other liabilities, Fair Value	497,336	332,869
Derivatives not designated as hedging instruments | Embedded derivative - IUL
Derivative [Line Items]
Other liabilities. Notional Amount	324,832	301,598
Other liabilities, Fair Value	196,655	151,765
Derivatives not designated as hedging instruments | Interest rate futures
Derivative [Line Items]
Other long-term investments, Notional Amounts	221,804	896,073
Other long-term investments, Fair Value	641	7,557
Other liabilities. Notional Amount	1,034,796	669,223
Other liabilities, Fair Value	1,960	10,375
Derivatives not designated as hedging instruments | Equity futures
Derivative [Line Items]
Other long-term investments, Notional Amounts	119,794	159,901
Other long-term investments, Fair Value	1,368	2,109
Other liabilities. Notional Amount	121,162	174,743
Other liabilities, Fair Value	2,016	2,376
Derivatives not designated as hedging instruments | Currency futures
Derivative [Line Items]
Other long-term investments, Notional Amounts	261,473	72,593
Other long-term investments, Fair Value	3,850	131
Other liabilities. Notional Amount	0	192,306
Other liabilities, Fair Value	0	1,836
Derivatives not designated as hedging instruments | Equity options
Derivative [Line Items]
Other long-term investments, Notional Amounts	7,379,220	6,685,670
Other long-term investments, Fair Value	661,507	676,257
Other liabilities. Notional Amount	5,249,748	4,827,714
Other liabilities, Fair Value	302,348	429,434
Derivatives not designated as hedging instruments | Other
Derivative [Line Items]
Other liabilities. Notional Amount	250,726	199,387
Other liabilities, Fair Value	44,153	53,245
Derivatives designated as hedging instrument | Cash flow hedges | Interest rate swaps
Derivative [Line Items]
Other liabilities. Notional Amount	350,000	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	$ 22,879	$ 11,373