INVESTMENT OPERATIONS - Schedule of Amortized Cost and Fair Value of the Company's Investments Classified as Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Amortized Cost	$ 62,470,798	$ 61,970,744
Gross Unrealized Gains	2,153,137	3,103,992
Gross Unrealized Losses	(2,221,232)	(325,660)
Fair Value	62,402,703	64,749,076
Residential mortgage-backed securities
Schedule of Investments [Line Items]
Amortized Cost	6,979,230	5,812,170
Gross Unrealized Gains	63,970	125,493
Gross Unrealized Losses	(112,660)	(6,322)
Fair Value	6,930,540	5,931,341
Commercial mortgage-backed securities
Schedule of Investments [Line Items]
Amortized Cost	2,527,869	2,588,575
Gross Unrealized Gains	45,074	54,385
Gross Unrealized Losses	(66,893)	(3,292)
Fair Value	2,506,050	2,639,668
Other asset-backed securities
Schedule of Investments [Line Items]
Amortized Cost	1,726,799	1,764,120
Gross Unrealized Gains	31,403	32,041
Gross Unrealized Losses	(103,164)	(14,926)
Fair Value	1,655,038	1,781,235
U.S. government-related securities
Schedule of Investments [Line Items]
Amortized Cost	1,000,140	1,032,048
Gross Unrealized Gains	30,154	5,664
Gross Unrealized Losses	(38)	(5,316)
Fair Value	1,030,256	1,032,396
Other government-related securities
Schedule of Investments [Line Items]
Amortized Cost	565,785	548,136
Gross Unrealized Gains	29,038	51,024
Gross Unrealized Losses	(15,422)	(1,991)
Fair Value	579,401	597,169
States, municipals, and political subdivisions
Schedule of Investments [Line Items]
Amortized Cost	4,301,818	4,415,008
Gross Unrealized Gains	271,882	225,072
Gross Unrealized Losses	(10,081)	(1,230)
Fair Value	4,563,619	4,638,850
Corporate securities
Schedule of Investments [Line Items]
Amortized Cost	44,352,067	44,493,799
Gross Unrealized Gains	1,681,608	2,603,636
Gross Unrealized Losses	(1,905,740)	(288,334)
Fair Value	44,127,935	46,809,101
Redeemable preferred stocks
Schedule of Investments [Line Items]
Amortized Cost	87,124	87,237
Gross Unrealized Gains	8	6,677
Gross Unrealized Losses	(7,234)	(4,249)
Fair Value	79,898	89,665
Fixed maturities
Schedule of Investments [Line Items]
Amortized Cost	61,540,832	60,741,093
Gross Unrealized Gains	2,153,137	3,103,992
Gross Unrealized Losses	(2,221,232)	(325,660)
Fair Value	61,472,737	63,519,425
Short-term investments
Schedule of Investments [Line Items]
Amortized Cost	929,966	1,229,651
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 929,966	$ 1,229,651

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Section 50
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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