Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 196	$ 271
Maximum Amount of Future Payments under Credit Default Swaps	$ 9,609	$ 11,520
Weighted Average Years to Maturity	4 years 9 months 18 days	4 years 3 months 18 days
Credit Risk Derivative Assets, at Fair Value	$ 196	$ 271
Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	32	39
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,987	$ 2,473
Weighted Average Years to Maturity	2 years 6 months	2 years 2 months 12 days
Aaa/Aa/A | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 4
Maximum Amount of Future Payments under Credit Default Swaps	$ 208	$ 298
Weighted Average Years to Maturity	2 years 8 months 12 days	1 year 8 months 12 days
Aaa/Aa/A | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 27	$ 35
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,779	$ 2,175
Weighted Average Years to Maturity	2 years 6 months	2 years 2 months 12 days
Baa
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 159	$ 206
Maximum Amount of Future Payments under Credit Default Swaps	$ 7,567	$ 8,755
Weighted Average Years to Maturity	5 years 4 months 24 days	4 years 10 months 24 days
Baa | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 3	$ 3
Maximum Amount of Future Payments under Credit Default Swaps	$ 249	$ 216
Weighted Average Years to Maturity	2 years 6 months	1 year 6 months
Baa | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 156	$ 203
Maximum Amount of Future Payments under Credit Default Swaps	$ 7,318	$ 8,539
Weighted Average Years to Maturity	5 years 6 months	5 years
Ba
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 0	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 0	$ 9
Weighted Average Years to Maturity	0 years	5 years
Ba | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 0	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 0	$ 9
Weighted Average Years to Maturity	0 years	5 years
B [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 26
Maximum Amount of Future Payments under Credit Default Swaps	$ 55	$ 283
Weighted Average Years to Maturity	5 years	4 years 9 months 18 days
B [Member] | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 0	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 0	$ 10
Weighted Average Years to Maturity	0 years	6 months
B [Member] | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 26
Maximum Amount of Future Payments under Credit Default Swaps	$ 55	$ 273
Weighted Average Years to Maturity	5 years	5 years