Reinsurance - Reinsurance Recoverables (Details) $ in Millions	3 Months Ended
Mar. 31, 2016 USD ($) Reinsurers	Dec. 31, 2015 USD ($)
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 6,725	$ 6,813
Reserve netted against reinsurance recoverables	$ 3
Minimum [Member] \| Standard Poors A Rating Or Better [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	90.00%
Guaranteed Minimum Income Benefit [Member]
Ceded Credit Risk [Line Items]
Number of external reinsurers	3	3
Berkshire Hathway Life Insurance Company Of Nebraska [Member] \| Guaranteed Minimum Death Benefits [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 1,156	$ 1,123
Berkshire Hathway Life Insurance Company Of Nebraska [Member] \| Guaranteed Minimum Death Benefits [Member] \| Ceded Credit Risk Secured [Member] \| Reinsurance Recoverable [Member]
Ceded Credit Risk [Line Items]
Concentration Risk, Percentage	100.00%
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	$ 3,659	3,705
Prudential Retirement Insurance And Annuity Company [Member] \| Retirement Benefits Business (sold in 2004) [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 976	995
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	$ 312	315
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, including U.S. Government [Member] \| Global Health Care, Global Supplemental Benefits, Group Disability and Life [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 497	553
Number of external reinsurers \| Reinsurers	80
U.S. Government [Member] \| Global Health Care, Global Supplemental Benefits, Group Disability and Life [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 100
Other Retrocessionaires [Member] \| Guaranteed Minimum Death Benefits [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 45	41
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] \| Global Health Care, Global Supplemental Benefits, Group Disability and Life [Member]
Ceded Credit Risk [Line Items]
Maximum reinsurance recoverable from a single reinsurer	$ 90
Other Retrocessionaires [Member] \| Global Health Care, Global Supplemental Benefits, Group Disability and Life [Member] \| Maximum [Member]
Ceded Credit Risk [Line Items]
Minimum reinsurance recoverable balance from a single reinsurer	$ 1
Other Retrocessionaires [Member] \| 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	18.00%
Other Retrocessionaires [Member] \| Other run-off reinsurance [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 80	$ 81
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

The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross reinsurance premiums receivable to net realizable value.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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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Namespace Prefix:	ci_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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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Namespace Prefix:	ci_
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Balance Type:	debit
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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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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=51801978&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=49121117&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=51801978&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=49121117&loc=d3e13537-108611

+ Details

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Period Type:	duration

- Definition

Amount after valuation allowance recoverable 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 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),6)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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