Derivative Instruments (Exposure from Credit Derivatives by Rating of the Underlying Credits) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2024	Dec. 31, 2023
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 1	$ 4
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 2,005	$ 1,475
Derivative Average Remaining Maturity	[1],[3]	7 years 7 months 6 days	8 years 6 months
Standard Poors AAA To A Minus Ratings [Member] | Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ (3)	$ 2
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 420	$ 420
Derivative Average Remaining Maturity	[1],[3]	17 years 9 months 18 days	18 years 1 month 6 days
Standard Poors BBB Rating [Member] | Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 4	$ 4
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 150	$ 165
Derivative Average Remaining Maturity	[1],[3]	2 years 7 months 6 days	2 years 9 months 18 days
Standard Poors BBB Rating [Member] | Credit Default Swaps Referencing Indices [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 0	$ (1)
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 1,410	$ 880
Derivative Average Remaining Maturity	[1],[3]	5 years 2 months 12 days	5 years
Standard Poors BBB Rating [Member] | Credit Default Subtotal [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 4	$ 3
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 1,560	$ 1,045
Derivative Average Remaining Maturity	[1],[3]	5 years	4 years 8 months 12 days
Standard & Poor's, BB Rating [Member]
Credit Derivatives [Line Items]
Derivative Average Remaining Maturity	[1],[3]	2 years 8 months 12 days	2 years 2 months 12 days
Standard & Poor's, BB Rating [Member] | Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 0	$ (1)
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 15	$ 10
Standard & Poor's, B Rating
Credit Derivatives [Line Items]
Derivative Average Remaining Maturity	[1],[3]	2 years	0 years
Standard & Poor's, B Rating | Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 0	$ 0
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 10	$ 0

[1] The rating agency designations are based on ratings from Standard and Poor’s (“S&P”).

[2] Assumes the value of the referenced credit obligations is zero.

[3] The weighted average years to maturity of the credit default swaps is calculated based on weighted average notional amounts.