Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Amortized cost	$ 9,343	$ 9,639
Estimated Fair Value
Estimated Fair Value	9,501	10,122
Fixed Maturities [Member]
Amortized Cost
Due within one year	300
Due after one year through five years	1,691
Due after five years through 10 years	2,028
Due after 10 years	3,255
Amortized cost	8,410	8,371
Estimated Fair Value
Due within one year	300
Due after one year through five years	1,694
Due after five years through 10 years	2,037
Due after 10 years	3,406
Estimated Fair Value	8,568	8,854
Fixed Maturities [Member] \| RMBS [Member]
Amortized Cost
Amortized cost	737	745
Estimated Fair Value
Estimated Fair Value	717	775
Fixed Maturities [Member] \| CMBS [Member]
Amortized Cost
Amortized cost	399	402
Estimated Fair Value
Estimated Fair Value	$ 414	$ 419

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
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