MRBs - Summary of Balances of Changes in Net MRB (Assets) Liabilities (Details) - USD ($) $ in Millions	6 Months Ended	9 Months Ended
	Jun. 30, 2025	Sep. 30, 2025	Sep. 30, 2024
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	$ (3,814)	$ (3,814)
Balance as of end-of-period		(3,504)
Variable Annuities
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	(3,804)	(3,804)	$ (2,180)
Balance as of beginning-of-period, before the effect of changes in non-performance risk	(3,651)	(3,651)	(881)
Issuances		12	6
Attributed fees collected		1,105	1,143
Benefit payments		(20)	(29)
Effect of changes in interest rates		75	(101)
Effect of changes in equity markets		(1,667)	(2,347)
Effect of changes in equity index volatility		36	(65)
In-force updates and other changes in MRBs		367	69
Effect of changes in future expected policyholder behavior	7	37
Effect of changes in other future expected assumptions	(199)	10
Balance as of end-of-year, before the effect of changes in non-performance risk		(3,696)	(2,397)
Effect of cumulative changes in non-performance risk		114	(930)
Balance as of end-of-period		(3,582)	(3,327)
Less: Ceded MRB assets (liabilities)		(347)	(340)
Balance as of end-of-period, net of reinsurance		$ (3,235)	$ (2,987)
Weighted-average age of policyholders (years)		73 years	72 years
Net amount at risk		$ 1,442	$ 1,544
Variable Annuities | Cumulative Effect, Period of Adoption, Adjustment
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	(153)	(153)	(1,299)
Fixed Annuities
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	32	32	32
Balance as of beginning-of-period, before the effect of changes in non-performance risk	65	65	90
Issuances		0	0
Attributed fees collected		23	24
Benefit payments		0	0
Effect of changes in interest rates		38	8
Effect of changes in equity markets		(6)	(16)
Effect of changes in equity index volatility		7	(4)
In-force updates and other changes in MRBs		19	3
Effect of changes in future expected policyholder behavior	11	15
Effect of changes in other future expected assumptions	18	0
Balance as of end-of-year, before the effect of changes in non-performance risk		161	134
Effect of cumulative changes in non-performance risk		(40)	(60)
Balance as of end-of-period		121	74
Less: Ceded MRB assets (liabilities)		0	0
Balance as of end-of-period, net of reinsurance		$ 121	$ 74
Weighted-average age of policyholders (years)		70 years	69 years
Net amount at risk		$ 288	$ 231
Fixed Annuities | Cumulative Effect, Period of Adoption, Adjustment
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	(33)	(33)	(58)
Retirement Plan Services
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	(42)	(42)	(30)
Balance as of beginning-of-period, before the effect of changes in non-performance risk	(42)	(42)	(26)
Issuances		0	0
Attributed fees collected		5	4
Benefit payments		0	0
Effect of changes in interest rates		(3)	(6)
Effect of changes in equity markets		(6)	(8)
Effect of changes in equity index volatility		0	0
In-force updates and other changes in MRBs		3	6
Effect of changes in future expected policyholder behavior	0	(1)
Effect of changes in other future expected assumptions	(6)	1
Balance as of end-of-year, before the effect of changes in non-performance risk		(43)	(36)
Effect of cumulative changes in non-performance risk		0	(4)
Balance as of end-of-period		(43)	(40)
Less: Ceded MRB assets (liabilities)		0	0
Balance as of end-of-period, net of reinsurance		$ (43)	$ (40)
Weighted-average age of policyholders (years)		63 years	63 years
Net amount at risk		$ 2	$ 3
Retirement Plan Services | Cumulative Effect, Period of Adoption, Adjustment
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	$ 0	$ 0	$ (4)