Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Investments (Rollforward of expected credit losses AFS) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 20	$ 0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Purchased with Credit Deterioration, Increase	5
Debt Securities, Available-for-sale, Allowance for Credit Loss, Period Increase (Decrease)	188
Debt Securities, Available-for-sale, Allowance for Credit Loss, Recovery	(193)
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff	(5)
Accounting Standards Update 2016-13 [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss				$ 25
Debt Securities, Available-for-sale, Allowance for Credit Loss, Period Increase (Decrease)	$ 11	$ 0	$ 0