Reinsurance - Reinsurance Recoverables (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) Reinsurers	Dec. 31, 2016 USD ($)
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 6,046	$ 6,478
Global Health Care, Global Supplemental Benefits, Group Disability and Life [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 454	478
Number of external reinsurers \| Reinsurers	90
Maximum reinsurance recoverable from a single reinsurer	$ 80
Global Health Care, Global Supplemental Benefits, Group Disability and Life [Member] \| Maximum [Member]
Ceded Credit Risk [Line Items]
Minimum reinsurance recoverable from a single reinsurer	$ 1
Global Health Care, Global Supplemental Benefits, Group Disability and Life [Member] \| Minimum [Member] \| Standard & Poor's Investment Grade [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	70.00%
Global Health Care, Global Supplemental Benefits, Group Disability and Life [Member] \| Ceded Credit Risk Secured [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	11.00%
Acquisition, disposition or runoff activities [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 5,592	6,000
The Lincoln National Life Insurance Company And Lincoln Life And Annuity Of New York [Member] \| Individual Life Insurance And Annuity (sold in 1998) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	3,436	3,586
Berkshire [Member] \| Guaranteed Minimum Death Benefits [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 928	1,085
Berkshire [Member] \| Guaranteed Minimum Death Benefits [Member] \| Ceded Credit Risk Secured [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	100.00%
Prudential Retirement Insurance And Annuity Company [Member] \| Retirement Benefits Business (sold in 2004) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 850	921
Prudential Retirement Insurance And Annuity Company [Member] \| Retirement Benefits Business (sold in 2004) [Member] \| Ceded Credit Risk Secured [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	100.00%
Great American Life Insurance Company [Member] \| Supplemental Benefits Business (2012 acquistion) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 283	297
Great American Life Insurance Company [Member] \| Supplemental Benefits Business (2012 acquistion) [Member] \| Ceded Credit Risk Secured [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	100.00%
Other Retrocessionaires [Member] \| Guaranteed Minimum Death Benefits [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 34	44
Other Retrocessionaires [Member] \| Guaranteed Minimum Death Benefits [Member] \| Ceded Credit Risk Secured [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	100.00%
Other Retrocessionaires [Member] \| Other run-off reinsurance [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 61	$ 67
Other Retrocessionaires [Member] \| Other run-off reinsurance [Member] \| Ceded Credit Risk Secured [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	100.00%

The number of external reinsurers underwriting credit risk ceded by the Company.

No definition available.

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- Definition

Out of a specified group or category, the maximum reinsurance recoverable from a single reinsurer.

+ References

No definition available.

+ Details

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- Definition

Out of a specified group or category, the minimum reinsurance recoverable balance from a single reinsurer.

+ References

No definition available.

+ Details

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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

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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- Definition

Amount, after valuation allowance, recoverable under reinsurance contracts including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21409-158489

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),6)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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