INVESTMENT OPERATIONS - Narrative (Details)	12 Months Ended
Dec. 31, 2018 USD ($) position reinsurer	Dec. 31, 2017 USD ($) reinsurer
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	$ 1,654,537,000	$ 601,185,000
Minimum percentage of underlying collateral guaranteed by third party	97.00%
Number of positions \| position	4,005
Fair Value	$ 49,898,408,000	39,488,434,000
Available-for-sale securities, amortized cost	52,452,334,000	39,455,935,000
Securities in trading portfolio	2,457,010,000	2,725,694,000
Non-income producing investments	140,500,000
Policy loans	$ 1,695,886,000	1,615,615,000
Interest rate on collateral loans on life insurance policies (as a percent)	13.64%
Minimum
Available-for-sale securities
Interest rate on standard policy loans (as a percent)	3.00%
Maximum
Available-for-sale securities
Interest rate on standard policy loans (as a percent)	8.00%
Below investment grade
Available-for-sale securities
Fair Value	$ 1,600,000,000
Available-for-sale securities, amortized cost	1,800,000,000
Securities in trading portfolio	144,300,000
Securities not publicly traded	262,800,000
Residential mortgage-backed securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	30,633,000	13,064,000
Commercial mortgage-backed securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	49,602,000	21,031,000
Other asset-backed securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	4,435,000	$ 5,441,000
Minimum percentage of underlying collateral guaranteed by third party		97.00%
U.S. government-related securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	41,054,000	$ 31,489,000
Other government-related securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	18,583,000	4,779,000
States, municipals, and political subdivisions
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	91,722,000	43,875,000
Corporate securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	1,411,415,000	471,752,000
Fixed Maturities
Available-for-sale securities
Fair Value	49,263,033,000
Available-for-sale securities, amortized cost	51,816,959,000
Gross Unrecognized Holding Losses	86,264,000	19,163,000
Gross Unrecognized Holding Gains	$ 0	$ 76,586,000
Red Mountain
Available-for-sale securities
Number of wholly owned subsidiaries which were determined to be VIE \| reinsurer	1	1
Ownership through an affiliate (as a percent)	100.00%
Risk of los related to the VIE limited to the entity's investment	$ 10,000
Payments made	$ 0

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 carrying amount of investments which do not generate any income.

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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 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 of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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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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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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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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