OPERATING SEGMENTS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summarized financial information for the company's segments
Revenues	$ 1,255,898	$ 1,269,963	$ 1,169,644	$ 1,063,511	$ 1,096,456	$ 1,105,392	$ 1,063,463	$ 1,047,356	$ 4,759,016	$ 4,312,667	$ 4,293,709
Pre-tax Adjusted Operating Income (Loss)									368,121	409,424	387,113
Realized gains (losses) on investments and derivatives									(120,533)	54,584	135,568
Income before income tax	69,588	95,170	60,894	21,936	78,096	165,982	133,286	86,644	247,588	464,008	522,681
Income tax expense (benefit)	24,728	16,646	8,626	3,661	(839,384)	49,016	43,654	28,305	53,661	(718,409)	170,073
Net income	44,860	78,524	52,268	18,275	917,480	116,966	89,632	58,339	193,927	1,182,417	352,608
Adjusted operating income tax (expense) benefit									(78,973)	737,513	(122,624)
After-tax adjusted operating income									289,148	1,146,937	264,489
Income tax (expense) benefit on adjustments									25,312	(19,104)	(47,449)
Realized investment (losses) gains:
Derivative financial instruments									79,097	(137,041)	49,790
Realized investment gains (losses) - investments									(223,276)	121,087	90,630
Net impairment losses recognized in earnings	(26,060)	(14)	(5)	(3,645)	(853)	(273)	(2,785)	(5,201)	(29,724)	(9,112)	(17,748)
Less: related amortization									(11,856)	(39,480)	24,360
Less: VA GMWB economic cost									(41,514)	(40,170)	(37,256)
Net investment income	639,115	$ 631,955	$ 578,414	$ 489,418	495,614	$ 477,011	$ 475,722	$ 474,709	2,338,902	1,923,056	1,823,463
Amortization of deferred policy acquisition costs and value of business acquired									226,066	79,443	150,298
Operating Segment Assets
Investments and other assets	84,918,374				75,451,948				84,918,374	75,451,948
DAC and VOBA	3,026,330				2,205,401				3,026,330	2,205,401	2,024,524
Other intangibles	612,854				662,916				612,854	662,916
Goodwill	825,511				793,470				825,511	793,470
Total assets	89,383,069				79,113,735				89,383,069	79,113,735
Life Marketing
Realized investment (losses) gains:
Net investment income									552,697	550,714	523,989
Amortization of deferred policy acquisition costs and value of business acquired									116,917	120,753	130,708
Operating Segment Assets
DAC and VOBA	1,499,386				1,320,776				1,499,386	1,320,776	1,218,944
Acquisitions
Realized investment (losses) gains:
Net investment income									1,108,218	752,520	764,571
Amortization of deferred policy acquisition costs and value of business acquired									18,690	(6,939)	8,178
Operating Segment Assets
DAC and VOBA	458,976				74,862				458,976	74,862	106,532
Annuities
Realized investment (losses) gains:
Net investment income									335,382	316,582	318,511
Amortization of deferred policy acquisition costs and value of business acquired									24,274	(54,471)	(11,031)
Operating Segment Assets
DAC and VOBA	889,697				772,633				889,697	772,633	655,618
Stable Value Products
Realized investment (losses) gains:
Net investment income									217,778	186,576	107,010
Amortization of deferred policy acquisition costs and value of business acquired									3,201	2,354	1,176
Operating Segment Assets
DAC and VOBA	6,121				6,864				6,121	6,864	5,455
Asset Protection
Realized investment (losses) gains:
Net investment income									25,070	22,298	17,591
Amortization of deferred policy acquisition costs and value of business acquired									62,984	17,746	21,267
Operating Segment Assets
DAC and VOBA	172,150				30,266				172,150	30,266	37,975
Corporate and Other
Realized investment (losses) gains:
Net investment income									99,757	94,366	91,791
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									4,759,016	4,312,667	4,293,709
Pre-tax Adjusted Operating Income (Loss)									368,121	409,424	387,113
Operating | Life Marketing
Summarized financial information for the company's segments
Revenues									1,567,857	1,556,207	1,517,542
Pre-tax Adjusted Operating Income (Loss)									(13,726)	55,152	41,457
Operating Segment Assets
Investments and other assets	14,607,822				14,917,752				14,607,822	14,917,752
DAC and VOBA	1,499,386				1,320,776				1,499,386	1,320,776
Other intangibles	262,181				281,705				262,181	281,705
Goodwill	215,254				200,274				215,254	200,274
Total assets	16,584,643				16,720,507				16,584,643	16,720,507
Operating | Acquisitions
Summarized financial information for the company's segments
Revenues									2,027,195	1,569,083	1,676,017
Pre-tax Adjusted Operating Income (Loss)									282,715	249,749	260,511
Operating Segment Assets
Investments and other assets	31,859,520				19,588,133				31,859,520	19,588,133
DAC and VOBA	458,977				74,862				458,977	74,862
Other intangibles	31,975				34,548				31,975	34,548
Goodwill	23,862				14,524				23,862	14,524
Total assets	32,374,334				19,712,067				32,374,334	19,712,067
Operating | Annuities
Summarized financial information for the company's segments
Revenues									478,114	486,847	547,512
Pre-tax Adjusted Operating Income (Loss)									129,155	171,269	174,362
Operating Segment Assets
Investments and other assets	20,160,279				20,774,566				20,160,279	20,774,566
DAC and VOBA	889,697				772,634				889,697	772,634
Other intangibles	156,785				170,117				156,785	170,117
Goodwill	343,247				336,677				343,247	336,677
Total assets	21,550,008				22,053,994				21,550,008	22,053,994
Operating | Stable Value Products
Summarized financial information for the company's segments
Revenues									219,501	190,006	114,580
Pre-tax Adjusted Operating Income (Loss)									102,328	105,261	61,294
Operating Segment Assets
Investments and other assets	5,107,334				4,569,639				5,107,334	4,569,639
DAC and VOBA	6,121				6,864				6,121	6,864
Other intangibles	7,389				8,056				7,389	8,056
Goodwill	113,924				113,813				113,924	113,813
Total assets	5,234,768				4,698,372				5,234,768	4,698,372
Operating | Asset Protection
Summarized financial information for the company's segments
Revenues									355,501	370,449	306,237
Pre-tax Adjusted Operating Income (Loss)									24,371	17,638	11,309
Operating Segment Assets
Investments and other assets	827,416				708,605				827,416	708,605
DAC and VOBA	172,149				30,265				172,149	30,265
Other intangibles	122,590				133,234				122,590	133,234
Goodwill	129,224				128,182				129,224	128,182
Total assets	1,251,379				1,000,286				1,251,379	1,000,286
Operating | Corporate and Other
Summarized financial information for the company's segments
Revenues									110,848	140,075	131,821
Pre-tax Adjusted Operating Income (Loss)									(156,722)	(189,645)	$ (161,820)
Operating Segment Assets
Investments and other assets	12,356,003				14,893,253				12,356,003	14,893,253
DAC and VOBA	0				0				0	0
Other intangibles	31,934				35,256				31,934	35,256
Goodwill	0				0				0	0
Total assets	$ 12,387,937				$ 14,928,509				$ 12,387,937	$ 14,928,509