Derivative Instruments (Exposure from Credit Derivatives by Rating of the Underlying Credits) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	[1]	$ 13	$ 5
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 1,517	$ 1,306
Derivative Average Remaining Maturity	[1],[3]	5 years 7 months 6 days	3 years 8 months 12 days
Standard Poors AAA To A Ratings [Member]
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	[1]	$ 11	$ 2
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 287	$ 142
Derivative Average Remaining Maturity	[1],[3]	15 years	1 year 8 months 12 days
Standard & Poor's, BBB Rating [Member]
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	[1]	$ 2	$ 3
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 1,220	$ 1,164
Derivative Average Remaining Maturity	[1],[3]	3 years 6 months	4 years
Standard & Poor's, BB+ Rating [Member]
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	[1]	$ 0	$ 0
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 10	$ 0
Derivative Average Remaining Maturity	[1],[3]	8 months 12 days	0 years
Single Name Credit Default Swaps [Member] | Standard Poors AAA To A Ratings [Member]
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	[1]	$ 11	$ 2
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 287	$ 142
Derivative Average Remaining Maturity	[1],[3]	15 years	1 year 8 months 12 days
Single Name Credit Default Swaps [Member] | Standard & Poor's, BBB Rating [Member]
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	[1]	$ 2	$ 3
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 232	$ 291
Derivative Average Remaining Maturity	[1],[3]	1 year 7 months 6 days	1 year 10 months 24 days
Single Name Credit Default Swaps [Member] | Standard & Poor's, BB+ Rating [Member]
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	[1]	$ 0	$ 0
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 10	$ 0
Derivative Average Remaining Maturity	[1],[3]	8 months 12 days	0 years
Credit Default Swaps Referencing Indices [Member] | Standard & Poor's, BBB Rating [Member]
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	[1]	$ 0	$ 0
Maximum Potential Future Exposure on Credit Risk Derivatives	[1],[2]	$ 988	$ 873
Derivative Average Remaining Maturity	[1],[3]	3 years 10 months 24 days	4 years 8 months 12 days

[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