MRBs - Summary of Balances of Changes in Net MRB (Assets) Liabilities (Details) - USD ($) $ in Millions	6 Months Ended	9 Months Ended
	Jun. 30, 2024	Sep. 30, 2024	Sep. 30, 2023
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	$ (2,178)	$ (2,178)
Balance as of end-of-period		(3,293)
Variable Annuities
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	(2,180)	(2,180)	$ (662)
Balance as of beginning-of-period, before the effect of changes in non-performance risk	(881)	(881)	1,511
Issuances		6	3
Attributed fees collected		1,143	1,127
Benefit payments		(29)	(49)
Effect of changes in interest rates		(101)	(2,347)
Effect of changes in equity markets		(2,347)	(1,430)
Effect of changes in equity index volatility		(65)	(358)
In-force updates and other changes in MRBs		69	182
Effect of changes in future expected policyholder behavior	(33)	7
Effect of changes in other future expected assumptions	(66)	(199)
Balance as of end-of-year, before the effect of changes in non-performance risk		(2,397)	(1,460)
Effect of cumulative changes in non-performance risk		(930)	(1,213)
Balance as of end-of-period		(3,327)	(2,673)
Less: ceded MRB assets (liabilities)		(340)	(303)
Balance as of end-of-period, net of reinsurance		$ (2,987)	$ (2,370)
Weighted-average age of policyholders (years)		72 years	72 years
Net amount at risk		$ 1,544	$ 6,235
Variable Annuities | Cumulative Effect, Period of Adoption, Adjustment
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	(1,299)	(1,299)	(2,173)
Fixed Annuities
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	32	32	(45)
Balance as of beginning-of-period, before the effect of changes in non-performance risk	90	90	(5)
Issuances		0	0
Attributed fees collected		24	23
Benefit payments		0	0
Effect of changes in interest rates		8	(66)
Effect of changes in equity markets		(16)	(5)
Effect of changes in equity index volatility		(4)	6
In-force updates and other changes in MRBs		3	4
Effect of changes in future expected policyholder behavior	70	11
Effect of changes in other future expected assumptions	15	18
Balance as of end-of-year, before the effect of changes in non-performance risk		134	42
Effect of cumulative changes in non-performance risk		(60)	(59)
Balance as of end-of-period		74	(17)
Less: ceded MRB assets (liabilities)		0	0
Balance as of end-of-period, net of reinsurance		$ 74	$ (17)
Weighted-average age of policyholders (years)		69 years	68 years
Net amount at risk		$ 231	$ 188
Fixed Annuities | Cumulative Effect, Period of Adoption, Adjustment
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	(58)	(58)	(40)
Retirement Plan Services
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	(30)	(30)	(22)
Balance as of beginning-of-period, before the effect of changes in non-performance risk	(26)	(26)	(20)
Issuances		0	0
Attributed fees collected		4	4
Benefit payments		0	0
Effect of changes in interest rates		(6)	(7)
Effect of changes in equity markets		(8)	(6)
Effect of changes in equity index volatility		0	(3)
In-force updates and other changes in MRBs		6	0
Effect of changes in future expected policyholder behavior	0	0
Effect of changes in other future expected assumptions	(2)	(6)
Balance as of end-of-year, before the effect of changes in non-performance risk		(36)	(34)
Effect of cumulative changes in non-performance risk		(4)	1
Balance as of end-of-period		(40)	(33)
Less: ceded MRB assets (liabilities)		0	0
Balance as of end-of-period, net of reinsurance		$ (40)	$ (33)
Weighted-average age of policyholders (years)		63 years	63 years
Net amount at risk		$ 3	$ 9
Retirement Plan Services | Cumulative Effect, Period of Adoption, Adjustment
Market Risk Benefit [Roll Forward]
Balance as of beginning-of-year	$ (4)	$ (4)	$ (2)