Derivatives - Credit Risk Assumed through Credit Derivatives (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Credit Derivatives [Line Items]
Notional Amount	$ 12,291	$ 12,730
Fair Value	(61)	(90)
Credit derivatives
Credit Derivatives [Line Items]
Notional Amount	1,123	1,346
Fair Value	(3)	0
Offsetting Notional Amount	21	523
Offsetting Fair Value	6	5
Credit derivatives \| Single name credit default swaps \| A Minus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Notional Amount	169	130
Fair Value	$ 2	$ 3
Weighted Average Years to Maturity	4 years	5 years
Offsetting Notional Amount	$ 0	$ 0
Offsetting Fair Value	0	0
Credit derivatives \| Single name credit default swaps \| B \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Notional Amount		9
Fair Value		0
Offsetting Notional Amount		9
Offsetting Fair Value		0
Credit derivatives \| Basket credit default swaps \| A Minus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Notional Amount	11
Fair Value	$ 0
Weighted Average Years to Maturity	5 years
Offsetting Notional Amount	$ 2
Offsetting Fair Value	0
Credit derivatives \| Basket credit default swaps \| BBB Plus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Notional Amount	799	1,137
Fair Value	$ (1)	$ 2
Weighted Average Years to Maturity	6 years	3 years
Offsetting Notional Amount	$ 0	$ 454
Offsetting Fair Value	0	(2)
Credit derivatives \| Basket credit default swaps \| B Plus \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Notional Amount	125	27
Fair Value	$ 2	$ 2
Weighted Average Years to Maturity	5 years	3 years
Offsetting Notional Amount	$ 0	$ 27
Offsetting Fair Value	0	0
Credit derivatives \| Basket credit default swaps \| A \| Investment grade risk exposure
Credit Derivatives [Line Items]
Notional Amount		13
Fair Value		$ (1)
Weighted Average Years to Maturity		5 years
Offsetting Notional Amount		$ 3
Offsetting Fair Value		0
Credit derivatives \| Basket credit default swaps \| CCC \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Notional Amount	19	30
Fair Value	(6)	(6)
Offsetting Notional Amount	19	30
Offsetting Fair Value	$ 6	$ 7

Derivative, Nominal Value, Amount Offset Against Collateral, Net

No definition available.

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- Definition

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

+ References

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

+ Details

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- Definition

Average period covered by credit risk derivative contracts, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ 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 (a)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5708775-113959

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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.

+ Details

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- Definition

The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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