Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 107	$ 271
Maximum Amount of Future Payments under Credit Default Swaps	$ 10,780	$ 11,520
Weighted Average Years to Maturity	4 years 3 months 18 days	4 years 3 months 18 days
Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 20	$ 39
Maximum Amount of Future Payments under Credit Default Swaps	$ 2,353	$ 2,473
Weighted Average Years to Maturity	2 years	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	$ 4	$ 4
Maximum Amount of Future Payments under Credit Default Swaps	$ 247	$ 298
Weighted Average Years to Maturity	1 year 10 months 24 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	$ 16	$ 35
Maximum Amount of Future Payments under Credit Default Swaps	$ 2,106	$ 2,175
Weighted Average Years to Maturity	2 years	2 years 2 months 12 days
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 89	$ 206
Maximum Amount of Future Payments under Credit Default Swaps	$ 8,254	$ 8,755
Weighted Average Years to Maturity	4 years 10 months 24 days	4 years 10 months 24 days
Baa [Member] | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 1	$ 3
Maximum Amount of Future Payments under Credit Default Swaps	$ 266	$ 216
Weighted Average Years to Maturity	2 years 4 months 24 days	1 year 6 months
Baa [Member] | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 88	$ 203
Maximum Amount of Future Payments under Credit Default Swaps	$ 7,988	$ 8,539
Weighted Average Years to Maturity	5 years	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	$ 20	$ 9
Weighted Average Years to Maturity	2 years 2 months 12 days	5 years
Ba | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (1)	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 20	$ 9
Weighted Average Years to Maturity	2 years 2 months 12 days	5 years
Ba | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Weighted Average Years to Maturity	0 years	0 years
B
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (1)	$ 26
Maximum Amount of Future Payments under Credit Default Swaps	$ 153	$ 283
Weighted Average Years to Maturity	4 years 7 months 6 days	4 years 9 months 18 days
B | 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 | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (1)	$ 26
Maximum Amount of Future Payments under Credit Default Swaps	$ 153	$ 273
Weighted Average Years to Maturity	4 years 7 months 6 days	5 years