OPERATING SEGMENTS - Schedule of Operating Segments (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($) numberOfSegments	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Summarized financial information for the company's segments
Number of operating segments | numberOfSegments					6
Revenues	$ 1,504,440		$ 1,419,093		$ 3,189,326	$ 2,783,898
Pre-tax Adjusted Operating Income (Loss)	116,540		104,847		174,422	213,653
Realized gains (losses) and adjustments	89,301		80,876		122,892	148,797
Income before income tax	205,841		185,723		297,314	362,450
Income tax expense	(40,736)		(31,309)		(58,244)	(65,938)
Net income	165,105	$ 73,965	154,414	$ 142,098	239,070	296,512
Adjusted operating income tax expense	(21,982)		(14,325)		(32,436)	(34,691)
After-tax adjusted operating income	94,558		90,522		141,986	178,962
Income tax (expense) benefit on adjustments	(18,754)		(16,984)		(25,808)	(31,247)
Realized gains (losses) and adjustments:
Derivative financial instruments	(160,578)		(55,266)		77,562	(128,574)
Investments	180,680		98,811		(95,571)	225,197
Less: related amortization	(55,952)		(26,840)		(114,378)	(31,201)
Less: VA GLWB economic cost	(13,247)		(10,491)		(26,523)	(20,973)
Net investment income	740,435		685,194		1,493,415	1,326,616
Amortization of deferred policy acquisition costs and value of business acquired	(18,508)		33,837		35,455	64,210
Operating Segment Assets
Investments and other assets	118,033,277				118,033,277		$ 115,549,177
DAC and VOBA	3,561,997				3,561,997		3,519,555
Other intangibles	565,115				565,115		583,426
Goodwill	825,511				825,511		825,511
Total assets	122,985,900				122,985,900		120,477,669
Retail Life and Annuity
Summarized financial information for the company's segments
Revenues	553,872		573,256		1,330,516	1,166,010
Pre-tax Adjusted Operating Income (Loss)	20,035		37,378		7,715	84,390
Realized gains (losses) and adjustments:
Net investment income	246,929		231,570		499,348	462,468
Amortization of deferred policy acquisition costs and value of business acquired	6,752		5,246		(7,004)	20,194
Operating Segment Assets
Investments and other assets	38,003,155				38,003,155		37,448,239
DAC and VOBA	2,503,881				2,503,881		2,416,616
Other intangibles	384,423				384,423		401,178
Goodwill	558,501				558,501		558,501
Total assets	41,449,960				41,449,960		40,824,534
Acquisitions
Summarized financial information for the company's segments
Revenues	797,561		667,031		1,597,162	1,276,973
Pre-tax Adjusted Operating Income (Loss)	97,997		69,810		173,122	144,722
Realized gains (losses) and adjustments:
Net investment income	413,346		355,761		829,773	680,272
Amortization of deferred policy acquisition costs and value of business acquired	(42,355)		12,037		9,606	10,961
Operating Segment Assets
Investments and other assets	54,020,299				54,020,299		54,074,450
DAC and VOBA	885,472				885,472		924,090
Other intangibles	34,668				34,668		36,321
Goodwill	23,862				23,862		23,862
Total assets	54,964,301				54,964,301		55,058,723
Stable Value Products
Summarized financial information for the company's segments
Revenues	52,539		67,585		89,141	127,164
Pre-tax Adjusted Operating Income (Loss)	16,665		28,106		41,990	50,345
Realized gains (losses) and adjustments:
Net investment income	52,399		67,122		115,069	124,743
Amortization of deferred policy acquisition costs and value of business acquired	770		854		1,567	1,727
Operating Segment Assets
Investments and other assets	5,858,557				5,858,557		5,317,885
DAC and VOBA	5,166				5,166		5,221
Other intangibles	6,389				6,389		6,722
Goodwill	113,924				113,924		113,924
Total assets	5,984,036				5,984,036		5,443,752
Asset Protection
Summarized financial information for the company's segments
Revenues	69,103		73,070		141,592	146,265
Pre-tax Adjusted Operating Income (Loss)	12,740		8,459		23,367	17,308
Realized gains (losses) and adjustments:
Net investment income	6,491		7,049		13,706	13,851
Amortization of deferred policy acquisition costs and value of business acquired	16,325		15,700		31,286	31,328
Operating Segment Assets
Investments and other assets	862,780				862,780		878,386
DAC and VOBA	167,478				167,478		173,628
Other intangibles	106,690				106,690		112,032
Goodwill	129,224				129,224		129,224
Total assets	1,266,172				1,266,172		1,293,270
Corporate and Other
Summarized financial information for the company's segments
Revenues	31,365		38,151		30,915	67,486
Pre-tax Adjusted Operating Income (Loss)	(30,897)		(38,906)		(71,772)	(83,112)
Realized gains (losses) and adjustments:
Net investment income	21,270		23,692		35,519	45,282
Amortization of deferred policy acquisition costs and value of business acquired	0		$ 0		0	$ 0
Operating Segment Assets
Investments and other assets	19,288,486				19,288,486		17,830,217
DAC and VOBA	0				0		0
Other intangibles	32,945				32,945		27,173
Goodwill	0				0		0
Total assets	$ 19,321,431				$ 19,321,431		$ 17,857,390