INVESTMENTS - Credit Quality (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total	$ 18,317	$ 18,154
Total accruing loans	18,064	17,901
Non-accruing Loans	253	253
Non-accruing Loans with No Allowance	0	0
Interest Income on Non-accruing Loans	0	7
Past Due
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	60	84
30-59 Days
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	1	39
60-89 Days
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	5	5
90 Days or More
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	54	40
Current
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	18,004	17,817
Total commercial and agricultural mortgage loans:
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	127	1,364
Fiscal year before current fiscal year	1,351	3,585
Two years before current fiscal year	3,527	2,445
Three years before current fiscal year	2,441	1,798
Four years before current fiscal year	1,782	826
Prior	7,903	7,207
Revolving Loans Amortized Cost Basis	579	500
Revolving Loans Converted to Term Loans Amortized Cost Basis	132	131
Total	17,842	17,856
Total commercial and agricultural mortgage loans: | Greater than 2.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	8	182
Fiscal year before current fiscal year	182	743
Two years before current fiscal year	743	1,161
Three years before current fiscal year	1,224	1,194
Four years before current fiscal year	1,192	269
Prior	3,752	3,435
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	7,101	6,984
Total commercial and agricultural mortgage loans: | 1.8x to 2.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	5	18
Fiscal year before current fiscal year	93	16
Two years before current fiscal year	16	238
Three years before current fiscal year	264	200
Four years before current fiscal year	196	194
Prior	720	723
Revolving Loans Amortized Cost Basis	318	383
Revolving Loans Converted to Term Loans Amortized Cost Basis	96	96
Total	1,708	1,868
Total commercial and agricultural mortgage loans: | 1.5x to 1.8x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	2	92
Fiscal year before current fiscal year	176	1,110
Two years before current fiscal year	960	265
Three years before current fiscal year	174	109
Four years before current fiscal year	110	179
Prior	1,225	1,117
Revolving Loans Amortized Cost Basis	100	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	2,747	2,872
Total commercial and agricultural mortgage loans: | 1.2x to 1.5x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	35	515
Fiscal year before current fiscal year	437	798
Two years before current fiscal year	1,091	605
Three years before current fiscal year	575	170
Four years before current fiscal year	159	109
Prior	1,345	1,203
Revolving Loans Amortized Cost Basis	79	41
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	3,721	3,441
Total commercial and agricultural mortgage loans: | 1.0x to 1.2x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	76	517
Fiscal year before current fiscal year	423	725
Two years before current fiscal year	336	106
Three years before current fiscal year	134	57
Four years before current fiscal year	57	69
Prior	771	601
Revolving Loans Amortized Cost Basis	82	76
Revolving Loans Converted to Term Loans Amortized Cost Basis	36	35
Total	1,915	2,186
Total commercial and agricultural mortgage loans: | Less than 1.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	1	40
Fiscal year before current fiscal year	40	193
Two years before current fiscal year	381	70
Three years before current fiscal year	70	68
Four years before current fiscal year	68	6
Prior	90	128
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	650	505
Total commercial and agricultural mortgage loans: | 0% - 50%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	14	293
Fiscal year before current fiscal year	352	326
Two years before current fiscal year	315	320
Three years before current fiscal year	319	270
Four years before current fiscal year	277	132
Prior	2,425	2,342
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	3,702	3,683
Total commercial and agricultural mortgage loans: | 50% - 70%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	113	763
Fiscal year before current fiscal year	759	2,062
Two years before current fiscal year	2,015	823
Three years before current fiscal year	820	951
Four years before current fiscal year	929	357
Prior	2,856	2,607
Revolving Loans Amortized Cost Basis	517	463
Revolving Loans Converted to Term Loans Amortized Cost Basis	96	96
Total	8,105	8,122
Total commercial and agricultural mortgage loans: | 70% - 90%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	308
Fiscal year before current fiscal year	240	1,197
Two years before current fiscal year	1,197	1,236
Three years before current fiscal year	1,144	523
Four years before current fiscal year	576	245
Prior	1,673	1,400
Revolving Loans Amortized Cost Basis	62	37
Revolving Loans Converted to Term Loans Amortized Cost Basis	36	35
Total	4,928	4,981
Total commercial and agricultural mortgage loans: | 90% plus
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Two years before current fiscal year	0	66
Three years before current fiscal year	158	54
Four years before current fiscal year	0	92
Prior	949	858
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	1,107	1,070
Commercial:
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	73	1,202
Fiscal year before current fiscal year	1,189	3,277
Two years before current fiscal year	3,223	2,102
Three years before current fiscal year	2,101	1,362
Four years before current fiscal year	1,360	636
Prior	6,643	6,101
Revolving Loans Amortized Cost Basis	579	500
Revolving Loans Converted to Term Loans Amortized Cost Basis	132	131
Total	15,300	15,311
Total accruing loans	15,066	15,077
Non-accruing Loans	234	234
Non-accruing Loans with No Allowance	0	0
Interest Income on Non-accruing Loans	0	7
Commercial: | Past Due
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	0	32
Commercial: | 30-59 Days
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	0	32
Commercial: | 60-89 Days
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	0	0
Commercial: | 90 Days or More
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	0	0
Commercial: | Current
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	15,066	15,045
Commercial: | Greater than 2.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	175
Fiscal year before current fiscal year	175	693
Two years before current fiscal year	693	1,125
Three years before current fiscal year	1,190	1,135
Four years before current fiscal year	1,133	249
Prior	3,556	3,256
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	6,747	6,633
Commercial: | 1.8x to 2.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	0
Fiscal year before current fiscal year	75	0
Two years before current fiscal year	0	182
Three years before current fiscal year	208	167
Four years before current fiscal year	167	171
Prior	637	662
Revolving Loans Amortized Cost Basis	318	383
Revolving Loans Converted to Term Loans Amortized Cost Basis	96	96
Total	1,501	1,661
Commercial: | 1.5x to 1.8x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	80
Fiscal year before current fiscal year	164	1,060
Two years before current fiscal year	911	234
Three years before current fiscal year	143	0
Four years before current fiscal year	0	162
Prior	1,016	924
Revolving Loans Amortized Cost Basis	100	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	2,334	2,460
Commercial: | 1.2x to 1.5x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	469
Fiscal year before current fiscal year	391	687
Two years before current fiscal year	981	457
Three years before current fiscal year	427	0
Four years before current fiscal year	0	11
Prior	912	838
Revolving Loans Amortized Cost Basis	79	41
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	2,790	2,503
Commercial: | 1.0x to 1.2x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	73	470
Fiscal year before current fiscal year	376	668
Two years before current fiscal year	281	38
Three years before current fiscal year	67	0
Four years before current fiscal year	0	43
Prior	464	317
Revolving Loans Amortized Cost Basis	82	76
Revolving Loans Converted to Term Loans Amortized Cost Basis	36	35
Total	1,379	1,647
Commercial: | Less than 1.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	8
Fiscal year before current fiscal year	8	169
Two years before current fiscal year	357	66
Three years before current fiscal year	66	60
Four years before current fiscal year	60	0
Prior	58	104
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	549	407
Commercial: | 0% - 50%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	191
Fiscal year before current fiscal year	250	164
Two years before current fiscal year	155	129
Three years before current fiscal year	129	35
Four years before current fiscal year	35	0
Prior	1,515	1,540
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	2,084	2,059
Commercial: | 50% - 70%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	73	703
Fiscal year before current fiscal year	699	1,916
Two years before current fiscal year	1,871	671
Three years before current fiscal year	670	750
Four years before current fiscal year	749	299
Prior	2,522	2,319
Revolving Loans Amortized Cost Basis	517	463
Revolving Loans Converted to Term Loans Amortized Cost Basis	96	96
Total	7,197	7,217
Commercial: | 70% - 90%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	308
Fiscal year before current fiscal year	240	1,197
Two years before current fiscal year	1,197	1,236
Three years before current fiscal year	1,144	523
Four years before current fiscal year	576	245
Prior	1,657	1,384
Revolving Loans Amortized Cost Basis	62	37
Revolving Loans Converted to Term Loans Amortized Cost Basis	36	35
Total	4,912	4,965
Commercial: | 90% plus
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Two years before current fiscal year	0	66
Three years before current fiscal year	158	54
Four years before current fiscal year	0	92
Prior	949	858
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	1,107	1,070
Agricultural:
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	54	162
Fiscal year before current fiscal year	162	308
Two years before current fiscal year	304	343
Three years before current fiscal year	340	436
Four years before current fiscal year	422	190
Prior	1,260	1,106
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	2,542	2,545
Total accruing loans	2,523	2,526
Non-accruing Loans	19	19
Non-accruing Loans with No Allowance	0	0
Interest Income on Non-accruing Loans	0	0
Agricultural: | Past Due
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	60	52
Agricultural: | 30-59 Days
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	1	7
Agricultural: | 60-89 Days
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	5	5
Agricultural: | 90 Days or More
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	54	40
Agricultural: | Current
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	2,463	2,474
Agricultural: | Greater than 2.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	8	7
Fiscal year before current fiscal year	7	50
Two years before current fiscal year	50	36
Three years before current fiscal year	34	59
Four years before current fiscal year	59	20
Prior	196	179
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	354	351
Agricultural: | 1.8x to 2.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	5	18
Fiscal year before current fiscal year	18	16
Two years before current fiscal year	16	56
Three years before current fiscal year	56	33
Four years before current fiscal year	29	23
Prior	83	61
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	207	207
Agricultural: | 1.5x to 1.8x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	2	12
Fiscal year before current fiscal year	12	50
Two years before current fiscal year	49	31
Three years before current fiscal year	31	109
Four years before current fiscal year	110	17
Prior	209	193
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	413	412
Agricultural: | 1.2x to 1.5x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	35	46
Fiscal year before current fiscal year	46	111
Two years before current fiscal year	110	148
Three years before current fiscal year	148	170
Four years before current fiscal year	159	98
Prior	433	365
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	931	938
Agricultural: | 1.0x to 1.2x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	3	47
Fiscal year before current fiscal year	47	57
Two years before current fiscal year	55	68
Three years before current fiscal year	67	57
Four years before current fiscal year	57	26
Prior	307	284
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	536	539
Agricultural: | Less than 1.0x
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	1	32
Fiscal year before current fiscal year	32	24
Two years before current fiscal year	24	4
Three years before current fiscal year	4	8
Four years before current fiscal year	8	6
Prior	32	24
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	101	98
Agricultural: | 0% - 50%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	14	102
Fiscal year before current fiscal year	102	162
Two years before current fiscal year	160	191
Three years before current fiscal year	190	235
Four years before current fiscal year	242	132
Prior	910	802
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	1,618	1,624
Agricultural: | 50% - 70%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	40	60
Fiscal year before current fiscal year	60	146
Two years before current fiscal year	144	152
Three years before current fiscal year	150	201
Four years before current fiscal year	180	58
Prior	334	288
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	908	905
Agricultural: | 70% - 90%
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Two years before current fiscal year	0	0
Three years before current fiscal year	0	0
Four years before current fiscal year	0	0
Prior	16	16
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	16	16
Agricultural: | 90% plus
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Two years before current fiscal year	0	0
Three years before current fiscal year	0	0
Four years before current fiscal year	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	0	0
Residential mortgages:
Financing Receivable, before Allowance for Credit Loss [Abstract]
Current fiscal year	0	98
Fiscal year before current fiscal year	277	121
Two years before current fiscal year	120	74
Three years before current fiscal year	74	2
Four years before current fiscal year	2	1
Prior	2	2
Total	475	298
Total accruing loans	475	298
Non-accruing Loans	0	0
Non-accruing Loans with No Allowance	0	0
Interest Income on Non-accruing Loans	0	0
Residential mortgages: | Past Due
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	0	0
Residential mortgages: | 30-59 Days
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	0	0
Residential mortgages: | 60-89 Days
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	0	0
Residential mortgages: | 90 Days or More
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	0	0
Residential mortgages: | Current
Financing Receivable, before Allowance for Credit Loss [Abstract]
Total accruing loans	$ 475	$ 298