Contractholder Funds - Account Values by Range of Guaranteed Minimum Credit Rating (Details) $ in Millions	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Policyholder Account Balance [Line Items]
Contractholder funds	$ 50,875	$ 48,798
1 Basis Point-50 Basis Points Above | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0001	0.0001
1 Basis Point-50 Basis Points Above | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0050	0.0050
51 Basis Points-150 Basis Points Above | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0051	0.0051
51 Basis Points-150 Basis Points Above | Maximum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0150	0.0150
Greater Than 150 Basis Points Above | Minimum
Policyholder Account Balance [Line Items]
Policyholder account balance, above guaranteed minimum crediting rate	0.0150	0.0150
Indexed annuities
Policyholder Account Balance [Line Items]
Contractholder funds	$ 27,862	$ 27,164	$ 24,766
Indexed annuities | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	23,355	22,965
Indexed annuities | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1,393	1,446
Indexed annuities | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	615	550
Indexed annuities | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	2,499	2,203
Indexed annuities | 0.00% to 1.50%
Policyholder Account Balance [Line Items]
Contractholder funds	26,515	26,315
Indexed annuities | 0.00% to 1.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	22,671	22,392
Indexed annuities | 0.00% to 1.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1,391	1,444
Indexed annuities | 0.00% to 1.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	522	526
Indexed annuities | 0.00% to 1.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1,931	1,953
Indexed annuities | 1.51% to 2.50%
Policyholder Account Balance [Line Items]
Contractholder funds	993	471
Indexed annuities | 1.51% to 2.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	331	196
Indexed annuities | 1.51% to 2.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1	1
Indexed annuities | 1.51% to 2.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	93	24
Indexed annuities | 1.51% to 2.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	568	250
Indexed annuities | Greater Than 2.50%
Policyholder Account Balance [Line Items]
Contractholder funds	354	378
Indexed annuities | Greater Than 2.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	353	377
Indexed annuities | Greater Than 2.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1	1
Indexed annuities | Greater Than 2.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	0	0
Indexed annuities | Greater Than 2.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	0	0
Fixed rate annuities
Policyholder Account Balance [Line Items]
Contractholder funds	14,486	13,443	9,358
Fixed rate annuities | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	910	921
Fixed rate annuities | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	33	35
Fixed rate annuities | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1,365	1,559
Fixed rate annuities | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	12,178	10,928
Fixed rate annuities | 0.00% to 1.50%
Policyholder Account Balance [Line Items]
Contractholder funds	12,659	11,851
Fixed rate annuities | 0.00% to 1.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	36	23
Fixed rate annuities | 0.00% to 1.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	24	25
Fixed rate annuities | 0.00% to 1.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1,340	1,532
Fixed rate annuities | 0.00% to 1.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	11,259	10,271
Fixed rate annuities | 1.51% to 2.50%
Policyholder Account Balance [Line Items]
Contractholder funds	488	489
Fixed rate annuities | 1.51% to 2.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	4	5
Fixed rate annuities | 1.51% to 2.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	7	8
Fixed rate annuities | 1.51% to 2.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	21	23
Fixed rate annuities | 1.51% to 2.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	456	453
Fixed rate annuities | Greater Than 2.50%
Policyholder Account Balance [Line Items]
Contractholder funds	1,339	1,103
Fixed rate annuities | Greater Than 2.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	870	893
Fixed rate annuities | Greater Than 2.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	2	2
Fixed rate annuities | Greater Than 2.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	4	4
Fixed rate annuities | Greater Than 2.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	463	204
Universal Life
Policyholder Account Balance [Line Items]
Contractholder funds	2,488	2,391	$ 2,112
Universal Life | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	2,454	2,348
Universal Life | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	11	21
Universal Life | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1	1
Universal Life | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	22	21
Universal Life | 0.00% to 1.50%
Policyholder Account Balance [Line Items]
Contractholder funds	2,113	2,013
Universal Life | 0.00% to 1.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	2,085	1,987
Universal Life | 0.00% to 1.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	6	5
Universal Life | 0.00% to 1.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	0	0
Universal Life | 0.00% to 1.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	22	21
Universal Life | 1.51% to 2.50%
Policyholder Account Balance [Line Items]
Contractholder funds	0	0
Universal Life | 1.51% to 2.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	0	0
Universal Life | 1.51% to 2.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	0	0
Universal Life | 1.51% to 2.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	0	0
Universal Life | 1.51% to 2.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	0	0
Universal Life | Greater Than 2.50%
Policyholder Account Balance [Line Items]
Contractholder funds	375	378
Universal Life | Greater Than 2.50% | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Contractholder funds	369	361
Universal Life | Greater Than 2.50% | 1 Basis Point-50 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	5	16
Universal Life | Greater Than 2.50% | 51 Basis Points-150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	1	1
Universal Life | Greater Than 2.50% | Greater Than 150 Basis Points Above
Policyholder Account Balance [Line Items]
Contractholder funds	$ 0	$ 0