Investments - Hybrid Securities (Details) - Equity securities [Member] - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Hybrid securities	$ 44	$ 49
Hybrid instruments, cost	$ 58	$ 61

This item represents a parenthetical disclosure for the cost of hybrid instruments.

No definition available.

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

- Definition

Line items represent reporting 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

+ Details

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Namespace Prefix:	invest_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value as of the balance sheet date of hybrid instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 15
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6437212&loc=d3e50806-113969

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
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Balance Type:
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