Investments - Commercial Mortgage Loan Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investments [Abstract]
Commercial mortgage loans maturing in 2017	$ 92
Commercial mortgage loans maturing in 2018	138
Commercial mortgage loans maturing in 2019	251
Commercial mortgage loans maturing in 2020	97
Commercial mortgage loans maturing in 2021 and thereafter	1,088
Commercial Mortgage Loans Commitments To Extend Credit	69
Commercial Mortgage Loans	$ 1,666	$ 1,864

Commitments to extend credit under commercial mortgage loan agreements.

No definition available.

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Period Type:	instant

- Definition

Amount of mortgage loans maturing after the fourth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

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- Definition

Amount of mortgage loans maturing in the forth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

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

- Definition

Amount of mortgage loans maturing in the third fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

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

- Definition

Amount of mortgage loans maturing in the second fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

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

- Definition

Amount of mortgage loans maturing in the next fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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