Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 175	$ 196
Maximum Amount of Future Payments under Credit Default Swaps	$ 8,739	$ 9,609
Weighted Average Years to Maturity	4 years 8 months 12 days	4 years 9 months 18 days
Credit Risk Derivative Assets, at Fair Value	$ 175	$ 196
Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	26	32
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,947	$ 1,987
Weighted Average Years to Maturity	1 year 10 months 24 days	2 years 6 months
Aaa/Aa/A | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 5
Maximum Amount of Future Payments under Credit Default Swaps	$ 169	$ 208
Weighted Average Years to Maturity	3 years 2 months 12 days	2 years 8 months 12 days
Aaa/Aa/A | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 21	$ 27
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,778	$ 1,779
Weighted Average Years to Maturity	1 year 8 months 12 days	2 years 6 months
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 147	$ 159
Maximum Amount of Future Payments under Credit Default Swaps	$ 6,620	$ 7,567
Weighted Average Years to Maturity	5 years 7 months 6 days	5 years 4 months 24 days
Baa [Member] | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 3
Maximum Amount of Future Payments under Credit Default Swaps	$ 152	$ 249
Weighted Average Years to Maturity	2 years 6 months	2 years 6 months
Baa [Member] | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 145	$ 156
Maximum Amount of Future Payments under Credit Default Swaps	$ 6,468	$ 7,318
Weighted Average Years to Maturity	5 years 8 months 12 days	5 years 6 months
B
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 5
Maximum Amount of Future Payments under Credit Default Swaps	$ 55	$ 55
Weighted Average Years to Maturity	4 years 2 months 12 days	5 years
B | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 5
Maximum Amount of Future Payments under Credit Default Swaps	$ 55	$ 55
Weighted Average Years to Maturity	4 years 2 months 12 days	5 years
Ba
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 1	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 102	$ 0
Weighted Average Years to Maturity	2 years	0 years
Ba | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 82	$ 0
Weighted Average Years to Maturity	1 year 6 months	0 years
Ba | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (1)	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 20	$ 0
Weighted Average Years to Maturity	4 years 2 months 12 days	0 years
Caa3
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (4)	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 15	$ 0
Weighted Average Years to Maturity	4 years 2 months 12 days	0 years
Caa3 | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (4)	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 15	$ 0
Weighted Average Years to Maturity	4 years 2 months 12 days	0 years