Derivative Instruments (Exposure from Credit Derivatives by Rating of the Underlying Credits) (Details) - USD ($) $ in Millions		6 Months Ended		9 Months Ended
		Jun. 30, 2021		Sep. 30, 2020		Dec. 31, 2020
Credit Derivatives [Line Items]
Document Period End Date		Jun. 30, 2021
Credit Derivative Current Fair Value	[1]	$ 35				$ 13
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 1,893				1,517
Derivative Average Remaining Maturity	[1],[3]	6 years 8 months 12 days		5 years 7 months 6 days
Standard Poors AAA To A Minus Ratings [Member] | Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 34				11
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 715				287
Derivative Average Remaining Maturity	[1],[3]	12 years 4 months 24 days		15 years
Standard Poors AAA To A Minus Ratings [Member] | Credit Default Subtotal [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 34				11
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 715				287
Derivative Average Remaining Maturity	[1],[3]	12 years 4 months 24 days		15 years
Standard Poors BBB Rating [Member] | Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 1				2
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 181				232
Derivative Average Remaining Maturity	[1],[3]	2 years		1 year 7 months 6 days
Standard Poors BBB Rating [Member] | Credit Default Swaps Referencing Indices [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 0				0
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 988				988
Derivative Average Remaining Maturity	[1],[3]	3 years 4 months 24 days		3 years 10 months 24 days
Standard Poors BBB Rating [Member] | Credit Default Subtotal [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	$ 1				2
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 1,169				1,220
Derivative Average Remaining Maturity	[1],[3]	3 years 2 months 12 days		3 years 6 months
Standard & Poor's, BB Rating [Member]
Credit Derivatives [Line Items]
Derivative Average Remaining Maturity	[1]	6 months	[3]	8 months 12 days	[2]
Standard & Poor's, BB Rating [Member] | 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]	9				10
Standard & Poor's, BB Rating [Member] | Credit Default Subtotal [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	[1]	0				0
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 9				$ 10

[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.