OPERATING SEGMENTS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summarized financial information for the company's segments
Revenues	$ 1,454,794	$ 1,681,993	$ 1,434,931	$ 1,380,351	$ 1,255,898	$ 1,269,963	$ 1,169,644	$ 1,063,511	$ 5,952,069	$ 4,759,016	$ 4,312,667
Pre-tax Adjusted Operating Income (Loss)									434,846	368,121	409,424
Realized gains (losses) on investments and derivatives									248,602	(120,533)	54,584
Income before income tax	81,157	239,841	185,723	176,727	69,588	95,170	60,894	21,936	683,448	247,588	464,008
Income tax expense (benefit)	15,109	49,417	31,309	34,629	24,728	16,646	8,626	3,661	130,464	53,661	(718,409)
Net income	66,048	190,424	154,414	142,098	44,860	78,524	52,268	18,275	552,984	193,927	1,182,417
Adjusted operating income tax (expense) benefit									(78,257)	(78,973)	737,513
After-tax adjusted operating income									356,589	289,148	1,146,937
Income tax (expense) benefit on adjustments									(52,207)	25,312	(19,104)
Realized investment gains (losses):
Derivative financial instruments									(131,459)	79,097	(137,041)
Realized investment gains (losses) - investments									342,998	(223,276)	121,087
Net impairment losses recognized in earnings	(19,795)	(10,818)	(698)	(3,142)	(26,060)	(14)	(5)	(3,645)	(34,453)	(29,724)	(9,112)
Less: related amortization									(23,021)	(11,856)	(39,480)
Less: VA GLWB economic cost									(48,495)	(41,514)	(40,170)
Net investment income	752,503	$ 739,711	$ 685,194	$ 641,422	639,115	$ 631,955	$ 578,414	$ 489,418	2,818,830	2,338,902	1,923,056
Amortization of deferred policy acquisition costs and value of business acquired									175,653	226,066	79,443
Operating Segment Assets
Investments and other assets	115,549,177				84,918,374				115,549,177	84,918,374
DAC and VOBA	3,519,555				3,026,330				3,519,555	3,026,330	2,205,401
Other intangibles	583,426				612,854				583,426	612,854
Goodwill	825,511				825,511				825,511	825,511
Total assets	120,477,669				89,383,069				120,477,669	89,383,069
Life Marketing
Realized investment gains (losses):
Net investment income									571,654	552,697	550,714
Amortization of deferred policy acquisition costs and value of business acquired									157,854	116,917	120,753
Operating Segment Assets
DAC and VOBA	1,486,699				1,499,386				1,486,699	1,499,386	1,320,776
Acquisitions
Realized investment gains (losses):
Net investment income									1,532,605	1,108,218	752,520
Amortization of deferred policy acquisition costs and value of business acquired									10,693	18,690	(6,939)
Operating Segment Assets
DAC and VOBA	924,090				458,976				924,090	458,976	74,862
Annuities
Realized investment gains (losses):
Net investment income									367,650	335,382	316,582
Amortization of deferred policy acquisition costs and value of business acquired									(58,907)	24,274	(54,471)
Operating Segment Assets
DAC and VOBA	929,917				889,697				929,917	889,697	772,633
Stable Value Products
Realized investment gains (losses):
Net investment income									243,775	217,778	186,576
Amortization of deferred policy acquisition costs and value of business acquired									3,382	3,201	2,354
Operating Segment Assets
DAC and VOBA	5,221				6,121				5,221	6,121	6,864
Asset Protection
Realized investment gains (losses):
Net investment income									28,291	25,070	22,298
Amortization of deferred policy acquisition costs and value of business acquired									62,631	62,984	17,746
Operating Segment Assets
DAC and VOBA	173,628				172,150				173,628	172,150	30,266
Corporate and Other
Realized investment gains (losses):
Net investment income									74,855	99,757	94,366
Amortization of deferred policy acquisition costs and value of business acquired									0	0	0
Operating Segment Assets
DAC and VOBA	0				0				0	0	0
Operating
Summarized financial information for the company's segments
Revenues									5,952,069	4,759,016	4,312,667
Pre-tax Adjusted Operating Income (Loss)									434,846	368,121	409,424
Operating | Life Marketing
Summarized financial information for the company's segments
Revenues									1,694,618	1,567,857	1,556,207
Pre-tax Adjusted Operating Income (Loss)									(26,697)	(13,726)	55,152
Operating Segment Assets
Investments and other assets	16,013,892				14,607,822				16,013,892	14,607,822
DAC and VOBA	1,486,699				1,499,386				1,486,699	1,499,386
Other intangibles	243,210				262,181				243,210	262,181
Goodwill	215,254				215,254				215,254	215,254
Total assets	17,959,055				16,584,643				17,959,055	16,584,643
Operating | Acquisitions
Summarized financial information for the company's segments
Revenues									2,901,650	2,027,195	1,569,083
Pre-tax Adjusted Operating Income (Loss)									346,825	282,715	249,749
Operating Segment Assets
Investments and other assets	54,074,450				31,859,520				54,074,450	31,859,520
DAC and VOBA	924,090				458,977				924,090	458,977
Other intangibles	36,321				31,975				36,321	31,975
Goodwill	23,862				23,862				23,862	23,862
Total assets	55,058,723				32,374,334				55,058,723	32,374,334
Operating | Annuities
Summarized financial information for the company's segments
Revenues									623,854	478,114	486,847
Pre-tax Adjusted Operating Income (Loss)									145,578	129,155	171,269
Operating Segment Assets
Investments and other assets	21,434,347				20,160,279				21,434,347	20,160,279
DAC and VOBA	929,917				889,697				929,917	889,697
Other intangibles	157,968				156,785				157,968	156,785
Goodwill	343,247				343,247				343,247	343,247
Total assets	22,865,479				21,550,008				22,865,479	21,550,008
Operating | Stable Value Products
Summarized financial information for the company's segments
Revenues									246,587	219,501	190,006
Pre-tax Adjusted Operating Income (Loss)									93,183	102,328	105,261
Operating Segment Assets
Investments and other assets	5,317,885				5,107,334				5,317,885	5,107,334
DAC and VOBA	5,221				6,121				5,221	6,121
Other intangibles	6,722				7,389				6,722	7,389
Goodwill	113,924				113,924				113,924	113,924
Total assets	5,443,752				5,234,768				5,443,752	5,234,768
Operating | Asset Protection
Summarized financial information for the company's segments
Revenues									353,896	355,501	370,449
Pre-tax Adjusted Operating Income (Loss)									37,205	24,371	17,638
Operating Segment Assets
Investments and other assets	878,386				827,416				878,386	827,416
DAC and VOBA	173,628				172,149				173,628	172,149
Other intangibles	112,032				122,590				112,032	122,590
Goodwill	129,224				129,224				129,224	129,224
Total assets	1,293,270				1,251,379				1,293,270	1,251,379
Operating | Corporate and Other
Summarized financial information for the company's segments
Revenues									131,464	110,848	140,075
Pre-tax Adjusted Operating Income (Loss)									(161,248)	(156,722)	$ (189,645)
Operating Segment Assets
Investments and other assets	17,830,217				12,356,003				17,830,217	12,356,003
DAC and VOBA	0				0				0	0
Other intangibles	27,173				31,934				27,173	31,934
Goodwill	0				0				0	0
Total assets	$ 17,857,390				$ 12,387,937				$ 17,857,390	$ 12,387,937