Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) $ in Millions	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated fair value	$ 41,397	$ 44,813
Fixed maturity securities \| Income Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated fair value	$ 583	$ 525
Measurement Input, Credit Spread \| Income Approach Valuation Technique \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt securities, available-for-sale, measurement Input	0.01	0.01
Measurement Input, Credit Spread \| Income Approach Valuation Technique \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt securities, available-for-sale, measurement Input	0.10	0.06
Measurement Input, Credit Spread \| Income Approach Valuation Technique \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt securities, available-for-sale, measurement Input	0.04	0.02

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=117815213&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=117815213&loc=d3e19207-110258

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+ References

No definition available.

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