Derivative Financial Instruments - CDS Notional Amounts by Credit Rating (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Credit Derivatives
Notional amount	$ 2,446	$ 2,399
Credit default contracts
Credit Derivatives
Notional amount	5	1
Fair value	0	0
Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	5	1
Fair value	0	0
AA \| Credit default contracts
Credit Derivatives
Notional amount	0	0
AA \| Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	0	0
A \| Credit default contracts
Credit Derivatives
Notional amount	0	0
A \| Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	0	0
BBB \| Credit default contracts
Credit Derivatives
Notional amount	0	0
BBB \| Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	0	0
BB and lower \| Credit default contracts
Credit Derivatives
Notional amount	5	1
BB and lower \| Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	$ 5	$ 1

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value of credit risk derivative asset after deduction of credit risk derivative liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5708775-113959

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