OPERATING SEGMENTS (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of former operating segments combined | segment									2
Number of operating segments | segment									6
Number of operating segments after combination | segment									1
Summarized financial information for the company's segments
Revenues	$ 1,474,869	$ 1,633,227	$ 1,504,440	$ 1,684,886	$ 1,438,904	$ 1,666,026	$ 1,419,093	$ 1,364,805	$ 6,297,422	$ 5,888,828	$ 4,759,016
Pre-tax Adjusted Operating Income (Loss)									360,347	434,846	368,121
Realized gains (losses) and adjustments									53,177	248,602	(120,533)
Income before income tax	43,598	72,612	205,841	91,473	81,157	239,841	185,723	176,727	413,524	683,448	247,588
Income tax expense (benefit)	68	12,850	40,736	17,508	15,109	49,417	31,309	34,629	71,162	130,464	53,661
Net income	43,530	59,762	165,105	73,965	66,048	190,424	154,414	142,098	342,362	552,984	193,927
Adjusted operating income tax (expense) benefit									(59,995)	(78,257)	(78,973)
After-tax adjusted operating income									300,352	356,589	289,148
Income tax (expense) benefit on adjustments									(11,167)	(52,207)	25,312
Realized gains (losses) and adjustments:
Derivative financial instruments									8,679	(131,459)	79,097
Realized investment gains (losses) - investments									(39,806)	308,545	(253,000)
Less: related amortization									(30,362)	(23,021)	(11,856)
Less: VA GLWB economic cost									(53,942)	(48,495)	(41,514)
Net investment income	651,377	$ 738,171	$ 740,435	$ 752,980	752,503	$ 739,711	$ 685,194	$ 641,422	2,882,963	2,818,830	2,338,902
Amortization of deferred policy acquisition costs and value of business acquired									208,472	175,653	226,066
Operating Segment Assets
Investments and other assets	121,667,369				115,549,177				121,667,369	115,549,177
DAC and VOBA	3,419,684				3,519,555				3,419,684	3,519,555	3,026,330
Other intangibles	540,370				583,426				540,370	583,426
Goodwill	825,511				825,511				825,511	825,511
Total assets	126,452,934				120,477,669				126,452,934	120,477,669
Retail Life and Annuity
Realized gains (losses) and adjustments:
Net investment income									1,008,016	939,304	888,079
Amortization of deferred policy acquisition costs and value of business acquired									116,021	98,947	141,191
Operating Segment Assets
DAC and VOBA	2,479,781				2,416,616				2,479,781	2,416,616	2,389,083
Acquisitions
Realized gains (losses) and adjustments:
Net investment income									1,648,122	1,532,605	1,108,218
Amortization of deferred policy acquisition costs and value of business acquired									23,445	10,693	18,690
Operating Segment Assets
DAC and VOBA	761,475				924,090				761,475	924,090	458,976
Stable Value Products
Realized gains (losses) and adjustments:
Net investment income									230,217	243,775	217,778
Amortization of deferred policy acquisition costs and value of business acquired									3,322	3,382	3,201
Operating Segment Assets
DAC and VOBA	8,336				5,221				8,336	5,221	6,121
Asset Protection
Realized gains (losses) and adjustments:
Net investment income									23,379	28,291	25,070
Amortization of deferred policy acquisition costs and value of business acquired									65,684	62,631	62,984
Operating Segment Assets
DAC and VOBA	170,092				173,628				170,092	173,628	172,150
Corporate and Other
Realized gains (losses) and adjustments:
Net investment income									(26,771)	74,855	99,757
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									6,297,422	5,888,828	4,759,016
Pre-tax Adjusted Operating Income (Loss)									360,347	434,846	368,121
Operating | Retail Life and Annuity
Summarized financial information for the company's segments
Revenues									2,567,305	2,318,472	2,045,971
Pre-tax Adjusted Operating Income (Loss)									65,092	118,881	115,429
Operating Segment Assets
Investments and other assets	40,689,134				37,448,239				40,689,134	37,448,239
DAC and VOBA	2,479,781				2,416,616				2,479,781	2,416,616
Other intangibles	367,144				401,178				367,144	401,178
Goodwill	558,501				558,501				558,501	558,501
Total assets	44,094,560				40,824,534				44,094,560	40,824,534
Operating | Acquisitions
Summarized financial information for the company's segments
Revenues									3,283,725	2,901,650	2,027,195
Pre-tax Adjusted Operating Income (Loss)									406,799	346,825	282,715
Operating Segment Assets
Investments and other assets	55,628,003				54,074,450				55,628,003	54,074,450
DAC and VOBA	761,475				924,090				761,475	924,090
Other intangibles	32,948				36,321				32,948	36,321
Goodwill	23,862				23,862				23,862	23,862
Total assets	56,446,288				55,058,723				56,446,288	55,058,723
Operating | Stable Value Products
Summarized financial information for the company's segments
Revenues									176,286	246,587	219,501
Pre-tax Adjusted Operating Income (Loss)									89,610	93,183	102,328
Operating Segment Assets
Investments and other assets	5,927,866				5,317,885				5,927,866	5,317,885
DAC and VOBA	8,336				5,221				8,336	5,221
Other intangibles	6,056				6,722				6,056	6,722
Goodwill	113,924				113,924				113,924	113,924
Total assets	6,056,182				5,443,752				6,056,182	5,443,752
Operating | Asset Protection
Summarized financial information for the company's segments
Revenues									275,405	290,655	355,501
Pre-tax Adjusted Operating Income (Loss)									41,845	37,205	24,371
Operating Segment Assets
Investments and other assets	880,738				878,386				880,738	878,386
DAC and VOBA	170,092				173,628				170,092	173,628
Other intangibles	101,349				112,032				101,349	112,032
Goodwill	129,224				129,224				129,224	129,224
Total assets	1,281,403				1,293,270				1,281,403	1,293,270
Operating | Corporate and Other
Summarized financial information for the company's segments
Revenues									(5,299)	131,464	110,848
Pre-tax Adjusted Operating Income (Loss)									(242,999)	(161,248)	$ (156,722)
Operating Segment Assets
Investments and other assets	18,541,628				17,830,217				18,541,628	17,830,217
DAC and VOBA	0				0				0	0
Other intangibles	32,873				27,173				32,873	27,173
Goodwill	0				0				0	0
Total assets	$ 18,574,501				$ 17,857,390				$ 18,574,501	$ 17,857,390