Investments - Realized capital gains and losses by transaction type (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments [Abstract]
Sales	$ 233	$ 147	$ 800	$ 359
Credit losses	10	(14)	(79)	(43)
Valuation of equity investments	231	24	(111)	851
Valuation and settlements of derivative instruments	(34)	40	72	16
Realized capital gains and losses	$ 440	$ 197	$ 682	$ 1,183

Allowance for Credit Loss, Credit Loss Recognized In Net Income

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- Definition

Amount of unrealized and realized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity), investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

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- Definition

Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117546-209714

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
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-Subparagraph (SX 210.7-04(3)(d))
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- Definition

Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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- References

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Amount of realized gain (loss) on investment.

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-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
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