Derivatives (Credit Risk on Freestanding Derivatives) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Credit Derivatives [Line Items]
Estimated Fair Value of Derivatives in a Net Liability Position (1)	$ 1,572	$ 1,532
Estimated Fair Value Of Incremental Collateral Provided Upon A One Notch Downgrade In The Company's Credit Rating	14	15
Estimated Fair Value Of Incremental Collateral Provided Upon A Downgrade In The Company's Credit Rating to a Level that Triggers Full Overnight Collateralization or Termination of the Derivative Position	15	20
Fixed maturity securities
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided:	1,784	1,701
Cash
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided:	0	0
Derivatives Subject to Credit- Contingent Provisions
Credit Derivatives [Line Items]
Estimated Fair Value of Derivatives in a Net Liability Position (1)	1,533	1,508
Estimated Fair Value Of Incremental Collateral Provided Upon A One Notch Downgrade In The Company's Credit Rating	14	15
Estimated Fair Value Of Incremental Collateral Provided Upon A Downgrade In The Company's Credit Rating to a Level that Triggers Full Overnight Collateralization or Termination of the Derivative Position	15	20
Derivatives Subject to Credit- Contingent Provisions \| Fixed maturity securities
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided:	1,734	1,675
Derivatives Subject to Credit- Contingent Provisions \| Cash
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided:	0	0
Derivatives Not Subject to Credit- Contingent Provisions
Credit Derivatives [Line Items]
Estimated Fair Value of Derivatives in a Net Liability Position (1)	39	24
Estimated Fair Value Of Incremental Collateral Provided Upon A One Notch Downgrade In The Company's Credit Rating	0	0
Estimated Fair Value Of Incremental Collateral Provided Upon A Downgrade In The Company's Credit Rating to a Level that Triggers Full Overnight Collateralization or Termination of the Derivative Position	0	0
Derivatives Not Subject to Credit- Contingent Provisions \| Fixed maturity securities
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided:	50	26
Derivatives Not Subject to Credit- Contingent Provisions \| Cash
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided:	$ 0	$ 0

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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- Definition

The aggregate fair value of assets needed to immediately settle the derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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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.

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- Definition

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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