Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost
Amortized Cost	$ 8,968	$ 9,055
Estimated Fair Value
Estimated Fair Value	9,388	9,624
Fixed-maturity securities
Amortized Cost
Due within one year	364
Due after one year through five years	1,586
Due after five years through 10 years	1,938
Due after 10 years	3,487
Amortized Cost	8,267	8,204
Estimated Fair Value
Due within one year	371
Due after one year through five years	1,700
Due after five years through 10 years	1,989
Due after 10 years	3,723
Estimated Fair Value	8,687	8,773
Fixed-maturity securities \| RMBS
Amortized Cost
Amortized Cost	541	571
Estimated Fair Value
Estimated Fair Value	530	566
Fixed-maturity securities \| CMBS
Amortized Cost
Amortized Cost	351	358
Estimated Fair Value
Estimated Fair Value	$ 374	$ 387

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
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-Section 50
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Amount of 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
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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