Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Amortized Cost	$ 9,953	$ 10,613
Estimated Fair Value
Estimated Fair Value	10,419	10,818
Fixed Maturities [Member]
Amortized Cost
Due within one year	274
Due after one year through five years	1,617
Due after five years through 10 years	2,133
Due after 10 years	3,493
Amortized Cost	8,811	9,884
Estimated Fair Value
Due within one year	275
Due after one year through five years	1,635
Due after five years through 10 years	2,242
Due after 10 years	3,779
Estimated Fair Value	9,277	10,089
Fixed Maturities [Member] \| RMBS [Member]
Amortized Cost
Amortized Cost	846	999
Estimated Fair Value
Estimated Fair Value	877	982
Fixed Maturities [Member] \| CMBS [Member]
Amortized Cost
Amortized Cost	448	542
Estimated Fair Value
Estimated Fair Value	$ 469	$ 539

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)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

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