OPERATING SEGMENTS - Schedule of Operating Segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Summarized financial information for the company's segments
Number of operating segments | segment			6
Revenues	$ 1,633,227	$ 1,666,026	$ 4,822,553	$ 4,449,924
Pre-tax Adjusted Operating Income (Loss)	77,414	100,162	251,836	313,815
Realized gains (losses) and adjustments	(4,802)	139,679	118,090	288,476
Income before income tax	72,612	239,841	369,926	602,291
Income tax expense	(12,850)	(49,417)	(71,094)	(115,355)
Net income	59,762	190,424	298,832	486,936
Adjusted operating income tax expense	(13,859)	(20,085)	(46,295)	(54,775)
After-tax adjusted operating income	63,555	80,077	205,541	259,040
Income tax (expense) benefit on adjustments	1,009	(29,332)	(24,799)	(60,580)
Realized gains (losses) and adjustments:
Derivative financial instruments	15,337	42,286	92,899	(86,288)
Investments	22,819	77,399	(72,752)	302,596
Less: related amortization	56,313	(6,205)	(58,065)	(37,406)
Less: VA GLWB economic cost	(13,355)	(13,789)	(39,878)	(34,762)
Net investment income	738,171	739,711	2,231,586	2,066,327
Amortization of deferred policy acquisition costs and value of business acquired	109,141	61,350	144,596	125,560
Operating Segment Assets
Investments and other assets	120,097,016		120,097,016		$ 115,549,177
DAC and VOBA	3,461,920		3,461,920		3,519,555
Other intangibles	553,084		553,084		583,426
Goodwill	825,511		825,511		825,511
Total assets	124,937,531		124,937,531		120,477,669
Retail Life and Annuity
Summarized financial information for the company's segments
Revenues	664,525	651,222	1,995,041	1,817,232
Pre-tax Adjusted Operating Income (Loss)	14,927	3,015	22,642	87,405
Realized gains (losses) and adjustments:
Net investment income	249,122	235,318	748,470	697,786
Amortization of deferred policy acquisition costs and value of business acquired	76,982	37,277	69,978	57,471
Operating Segment Assets
Investments and other assets	39,070,453		39,070,453		37,448,239
DAC and VOBA	2,476,357		2,476,357		2,416,616
Other intangibles	375,851		375,851		401,178
Goodwill	558,501		558,501		558,501
Total assets	42,481,162		42,481,162		40,824,534
Acquisitions
Summarized financial information for the company's segments
Revenues	802,200	859,524	2,399,362	2,136,497
Pre-tax Adjusted Operating Income (Loss)	64,999	103,210	238,121	247,932
Realized gains (losses) and adjustments:
Net investment income	405,458	426,510	1,235,231	1,106,782
Amortization of deferred policy acquisition costs and value of business acquired	14,114	7,388	23,720	18,349
Operating Segment Assets
Investments and other assets	54,395,295		54,395,295		54,074,450
DAC and VOBA	808,377		808,377		924,090
Other intangibles	33,831		33,831		36,321
Goodwill	23,862		23,862		23,862
Total assets	55,261,365		55,261,365		55,058,723
Stable Value Products
Summarized financial information for the company's segments
Revenues	48,081	59,954	137,222	187,118
Pre-tax Adjusted Operating Income (Loss)	20,129	20,863	62,119	71,208
Realized gains (losses) and adjustments:
Net investment income	54,210	59,707	169,279	184,450
Amortization of deferred policy acquisition costs and value of business acquired	872	857	2,439	2,584
Operating Segment Assets
Investments and other assets	5,889,432		5,889,432		5,317,885
DAC and VOBA	7,681		7,681		5,221
Other intangibles	6,222		6,222		6,722
Goodwill	113,924		113,924		113,924
Total assets	6,017,259		6,017,259		5,443,752
Asset Protection
Summarized financial information for the company's segments
Revenues	68,198	72,729	209,790	218,995
Pre-tax Adjusted Operating Income (Loss)	9,484	9,637	32,851	26,945
Realized gains (losses) and adjustments:
Net investment income	5,438	7,164	19,144	21,015
Amortization of deferred policy acquisition costs and value of business acquired	17,173	15,828	48,459	47,156
Operating Segment Assets
Investments and other assets	869,456		869,456		878,386
DAC and VOBA	169,505		169,505		173,628
Other intangibles	104,019		104,019		112,032
Goodwill	129,224		129,224		129,224
Total assets	1,272,204		1,272,204		1,293,270
Corporate and Other
Summarized financial information for the company's segments
Revenues	50,223	22,597	81,138	90,082
Pre-tax Adjusted Operating Income (Loss)	(32,125)	(36,563)	(103,897)	(119,675)
Realized gains (losses) and adjustments:
Net investment income	23,943	11,012	59,462	56,294
Amortization of deferred policy acquisition costs and value of business acquired	0	$ 0	0	$ 0
Operating Segment Assets
Investments and other assets	19,872,380		19,872,380		17,830,217
DAC and VOBA	0		0		0
Other intangibles	33,161		33,161		27,173
Goodwill	0		0		0
Total assets	$ 19,905,541		$ 19,905,541		$ 17,857,390