Derivatives - Credit Risk Assumed through Credit Derivatives (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Credit Derivatives [Line Items]
Derivative, Notional Amount	$ 5,769	$ 7,081
Fair Value	(2)	45
Credit derivatives
Credit Derivatives [Line Items]
Derivative, Notional Amount	493	493
Fair Value	28	29
Derivative, Nominal Value, Amount Offset Against Collateral, Net	493	493
Offsetting Fair Value	(28)	(29)
Standard & Poor's, AAA Rating [Member] | Basket credit default swaps | Credit derivatives | Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	100	100
Fair Value	$ 1	$ 0
Weighted Average Years to Maturity	3 years	4 years
Derivative, Nominal Value, Amount Offset Against Collateral, Net	$ 100	$ 100
Offsetting Fair Value	(1)	0
Standard & Poor's, BB- Rating | Basket credit default swaps | Credit derivatives | Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	392
Fair Value	$ 28
Weighted Average Years to Maturity	3 years
Derivative, Nominal Value, Amount Offset Against Collateral, Net	$ 392
Offsetting Fair Value	(28)
Standard & Poor's, B+ Rating | Basket credit default swaps | Credit derivatives | Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		392
Fair Value		$ 30
Weighted Average Years to Maturity		3 years
Derivative, Nominal Value, Amount Offset Against Collateral, Net		$ 392
Offsetting Fair Value		(30)
Standard & Poor's, CCC+ Rating | Basket credit default swaps | Credit derivatives | Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount	1
Fair Value	$ (1)
Average Term of Credit Risk Derivatives Less than 1 Year	Less than 1 year
Derivative, Nominal Value, Amount Offset Against Collateral, Net	$ 1
Offsetting Fair Value	$ 1
Standard & Poor's, CCC Rating | Basket credit default swaps | Credit derivatives | Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		1
Fair Value		$ (1)
Average Term of Credit Risk Derivatives Less than 1 Year		Less than 1 year
Derivative, Nominal Value, Amount Offset Against Collateral, Net		$ 1
Offsetting Fair Value		$ 1