Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) $ in Millions	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated Fair Value (In millions)	$ 47,106	$ 47,412
Fixed maturity securities \| Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated Fair Value (In millions)	$ 1,154	$ 966
Measurement Input, Credit Spread \| Income Approach Valuation Technique \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range (Weighted Average)	0.01	0.01
Measurement Input, Credit Spread \| Income Approach Valuation Technique \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range (Weighted Average)	0.07	0.08
Measurement Input, Credit Spread \| Income Approach Valuation Technique \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range (Weighted Average)	0.02	0.03

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

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Value of input used to measure investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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