Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Estimated Fair Value
Amortized Cost	$ 10,613	$ 10,814
Estimated fair value	10,818	11,301
Fixed Maturities [Member]
Amortized Cost
Due within one year	206
Due after one year through five years	1,507
Due after five years through 10 years	2,387
Due after 10 years	4,243
Estimated Fair Value
Due within one year	203
Due after one year through five years	1,497
Due after five years through 10 years	2,393
Due after 10 years	4,475
Amortized Cost	9,884	10,187
Estimated fair value	10,089	10,674
Fixed Maturities [Member] \| Residential Mortgage-Backed Securities (RMBS) [Member]
Estimated Fair Value
Amortized Cost	999	852
Estimated fair value	982	861
Fixed Maturities [Member] \| Commercial Mortgage Backed Securities (CMBS) [Member]
Estimated Fair Value
Amortized Cost	542	540
Estimated fair value	$ 539	$ 549

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=82897076&loc=d3e27161-111563

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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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
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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