Market Risk Benefits - Reconciliation of the Market Risk Benefits Balance (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Market Risk Benefit [Line Items]
Market risk benefit assets, at fair value	$ 8,025	$ 6,737
Market risk benefit liabilities, at fair value	3,843	4,785
Market risk benefit - net (asset) liability	(4,182)	(1,952)
Variable annuity
Market Risk Benefit [Line Items]
Market risk benefit assets, at fair value	8,020	6,732
Market risk benefit liabilities, at fair value	3,794	4,732
Market risk benefit - net (asset) liability	(4,226)	(2,000)	$ 767
Other Product Lines
Market Risk Benefit [Line Items]
Market risk benefit assets, at fair value	5	5
Market risk benefit liabilities, at fair value	49	53
Market risk benefit - net (asset) liability	$ 44	$ 48