INVESTMENT OPERATIONS - Additional Information (Details)	12 Months Ended
Dec. 31, 2018 USD ($) subsidiary position	Dec. 31, 2017 USD ($) subsidiary
Variable Interest Entities
Gross unrealized losses, 12 Months or More	$ 1,658,939,000	$ 602,685,000
Number of positions in unrealized loss position \| position	4,005
Fixed maturity securities—available-for-sale	$ 50,264,864,000	39,819,928,000
Available-for-sale securities, amortized cost	52,826,470,000	39,783,880,000
Fixed maturity securities—trading	2,457,010,000	2,725,694,000
Held-to-maturity securities, unrecognized holding gain	86,300,000
Non-income producing securities	140,500,000
Policy loans	$ 1,695,886,000	$ 1,615,615,000
Interest rate on collateral loans on life insurance policies	13.64%
Number of wholly owned subsidiaries that were determined to be VIEs \| subsidiary	2
Red Mountain LLC
Variable Interest Entities
Number of wholly owned subsidiaries that were determined to be VIEs \| subsidiary		2
Ownership through an affiliate (as a percent)	100.00%
Risk of loss related to the VIE limited to the entity's investment	$ 10,000
Payments made	$ 0
Steel City LLC
Variable Interest Entities
Ownership through an affiliate (as a percent)	100.00%
Risk of loss related to the VIE limited to the entity's investment	$ 10,000
Payments made	0
Fixed maturities
Variable Interest Entities
Fixed maturity securities—available-for-sale	49,488,507,000
Available-for-sale securities, amortized cost	52,050,113,000
Fixed maturity securities—trading	2,416,192,000	$ 2,664,189,000
Held-to-maturity securities, accumulated unrecognized holding gain	0	76,586,000
Held-to-maturity securities, accumulated unrecognized holding loss	86,264,000	19,163,000
Equity securities
Variable Interest Entities
Gross unrealized losses, 12 Months or More		7,370,000
Fixed maturity securities—trading	9,892,000	5,244,000
Short-term investments
Variable Interest Entities
Fixed maturity securities—trading	30,926,000	56,261,000
Residential mortgage-backed securities
Variable Interest Entities
Gross unrealized losses, 12 Months or More	30,894,000	13,362,000
Fixed maturity securities—trading	241,836,000	259,694,000
Commercial mortgage-backed securities
Variable Interest Entities
Gross unrealized losses, 12 Months or More	50,659,000	21,594,000
Fixed maturity securities—trading	188,925,000	146,804,000
Other asset-backed securities
Variable Interest Entities
Gross unrealized losses, 12 Months or More	$ 4,435,000	$ 5,441,000
Percentage of underlying collateral of student-loan backed auction rate securities guaranteed by the Federal Family Education Loan Program (at least)	97.00%	97.00%
Fixed maturity securities—trading	$ 159,907,000	$ 138,097,000
U.S. government-related securities
Variable Interest Entities
Gross unrealized losses, 12 Months or More	41,054,000	31,489,000
Fixed maturity securities—trading	59,794,000	27,234,000
Other government-related securities
Variable Interest Entities
Gross unrealized losses, 12 Months or More	18,583,000	4,778,000
Fixed maturity securities—trading	44,207,000	63,925,000
States, municipals, and political subdivisions
Variable Interest Entities
Gross unrealized losses, 12 Months or More	91,722,000	43,874,000
Fixed maturity securities—trading	286,413,000	326,925,000
Corporate securities
Variable Interest Entities
Gross unrealized losses, 12 Months or More	1,414,499,000	472,394,000
Fixed maturity securities—trading	1,423,833,000	$ 1,698,183,000
Below investment grade
Variable Interest Entities
Fixed maturity securities—available-for-sale	1,600,000,000
Available-for-sale securities, amortized cost	1,800,000,000
Fixed maturity securities—trading	144,300,000
Securities not publicly traded	$ 262,800,000
Minimum
Variable Interest Entities
Interest rate on standard policy loans	3.00%
Maximum
Variable Interest Entities
Interest rate on standard policy loans	8.00%

Represents the interest rate on collateral loans on life insurance policies.

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Represents the interest rate on standard insurance policy loans receivable.

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Represents the number of wholly owned subsidiaries which were determined to be variable interest entities.

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Represents the minimum percentage of the underlying collateral guaranteed by a third party.

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Represents the value of securities that are not publicly traded.

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Represents the amount of payments made or required to be made related to the guarantee.

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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 accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position.

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Amount before allowance of loans made to policy and contract holders using their life insurance contracts' cash value or separate accounts as collateral. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums over and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

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