Derivatives - Credit Risk Assumed through Credit Derivatives (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Credit Derivatives [Line Items]
Derivative, Notional Amount	$ 7,689	$ 12,363
Fair Value	25	7
Credit derivatives
Credit Derivatives [Line Items]
Derivative, Notional Amount	498	499
Fair Value	28	22
Derivative, Nominal Value, Amount Offset Against Collateral, Net	498	499
Offsetting Fair Value	(28)	(22)
Standard & Poor's, AAA Rating [Member] | Basket credit default swaps | Credit derivatives | Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	101	101
Fair Value	$ (1)	$ (1)
Weighted Average Years to Maturity	4 years	5 years
Derivative, Nominal Value, Amount Offset Against Collateral, Net	$ 101	$ 101
Offsetting Fair Value	1	1
Standard & Poor's, B+ Rating | Basket credit default swaps | Credit derivatives | Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	396	396
Fair Value	$ 30	$ 24
Weighted Average Years to Maturity	4 years
Average Term of Credit Risk Derivatives Less than 1 Year		4 years
Derivative, Nominal Value, Amount Offset Against Collateral, Net	$ 396	$ 396
Offsetting Fair Value	(30)	(24)
CCC Minus | Basket credit default swaps | Credit derivatives | Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	1	2
Fair Value	$ (1)	$ (1)
Average Term of Credit Risk Derivatives Less than 1 Year	Less than 1 year	Less than 1 year
Derivative, Nominal Value, Amount Offset Against Collateral, Net	$ 1	$ 2
Offsetting Fair Value	$ 1	$ 1