INVESTMENT OPERATIONS - Narrative (Details)	12 Months Ended
Dec. 31, 2019 USD ($) reinsurer position	Dec. 31, 2018 USD ($) reinsurer
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	$ (239,860,000)	$ (1,654,537,000)
Minimum percentage of underlying collateral guaranteed by third party	97.00%
Number of positions \| position	876
Fixed maturity securities - available-for-sale	$ 64,746,076,000	49,898,408,000
Available-for-sale securities, amortized cost	61,970,744,000	52,452,334,000
Securities in trading portfolio	2,625,436,000	2,457,010,000
Non-income producing investments	155,100,000	140,500,000
Policy loans	$ 1,675,121,000	1,695,886,000
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
Fixed maturity securities - available-for-sale	$ 1,600,000,000
Available-for-sale securities, amortized cost	1,700,000,000
Securities in trading portfolio	124,400,000
Securities not publicly traded	227,000,000.0
Residential mortgage-backed securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	(2,091,000)	(30,633,000)
Fixed maturity securities - available-for-sale	5,931,341,000	3,602,991,000
Available-for-sale securities, amortized cost	5,812,170,000	3,641,678,000
Securities in trading portfolio	209,521,000	241,836,000
Commercial mortgage-backed securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	(1,571,000)	(49,602,000)
Fixed maturity securities - available-for-sale	2,639,668,000	2,266,387,000
Available-for-sale securities, amortized cost	2,588,575,000	2,319,476,000
Securities in trading portfolio	201,284,000	188,925,000
Other asset-backed securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	(8,410,000)	(4,435,000)
Fixed maturity securities - available-for-sale	1,781,235,000	1,391,893,000
Available-for-sale securities, amortized cost	1,764,120,000	1,410,059,000
Securities in trading portfolio	143,361,000	159,907,000
U.S. government-related securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	(1,943,000)	(41,054,000)
Fixed maturity securities - available-for-sale	1,032,396,000	1,614,505,000
Available-for-sale securities, amortized cost	1,032,048,000	1,658,433,000
Securities in trading portfolio	47,067,000	59,794,000
Other government-related securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	(1,322,000)	(18,583,000)
Fixed maturity securities - available-for-sale	597,169,000	514,036,000
Available-for-sale securities, amortized cost	548,136,000	543,534,000
Securities in trading portfolio	28,775,000	44,207,000
States, municipals, and political subdivisions
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	(229,000)	(91,722,000)
Fixed maturity securities - available-for-sale	4,638,850,000	3,588,841,000
Available-for-sale securities, amortized cost	4,415,008,000	3,682,037,000
Securities in trading portfolio	293,791,000	286,413,000
Corporate securities
Available-for-sale securities
Continuous unrealized loss position, 12 months or longer	(220,045,000)	(1,411,415,000)
Fixed maturity securities - available-for-sale	46,809,101,000	36,201,578,000
Available-for-sale securities, amortized cost	44,493,799,000	38,467,380,000
Securities in trading portfolio	1,590,936,000	1,423,833,000
Fixed Maturities
Available-for-sale securities
Fixed maturity securities - available-for-sale	63,516,425,000	49,263,033,000
Available-for-sale securities, amortized cost	60,741,093,000	51,816,959,000
Securities in trading portfolio	2,527,567,000	2,416,192,000
Gross unrealized holding gains	201,909,000	0
Gross unrecognized holding losses	$ 0	$ 86,264,000
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 loss 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 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, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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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, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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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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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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