Reinsurance - Account Value, Net Amount at Risk and Contractholders for GMDB Business (Details) - Variable Annuity - GMDB contractholder in Thousands, $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($) contractholder	Dec. 31, 2019 USD ($) contractholder
Net Amount at Risk by Product and Guarantee [Line Items]
Account value	$ 9,523	$ 9,110
Net amount at risk	$ 1,570	$ 1,764
Average attained age of contractholders (weighted by exposure)	77 years	76 years
Number of contractholders (estimated) \| contractholder	185	200

Total number of underlying contractholders for the Guaranteed Minimum Death Benefit business.

No definition available.

Name:	ci_GuaranteedMinimumDeathBenefitsTotalContractholders
Namespace Prefix:	ci_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of the general accounts corresponding to the specified product, guarantee type and subset of the guarantee.

+ References

+ Details

Name:	us-gaap_NetAmountAtRiskByProductAndGuaranteeGeneralAccountValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

Name:	us-gaap_NetAmountAtRiskByProductAndGuaranteeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Net amount at risk, representing the guaranteed benefit in excess of the current account balance corresponding to the specified product, guarantee type and subset of the guarantee.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 80
-Section 50
-Paragraph 1
-Subparagraph (d)(3),(5)
-URI http://asc.fasb.org/extlink&oid=121641442&loc=d3e19393-158473

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121639652&loc=d3e7104-158389

+ Details

Name:	us-gaap_NetAmountAtRiskByProductAndGuaranteeNetAmountAtRisk
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average attained age of policyholders or contract holders in the specified guarantee type and subset of guarantee class, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 80
-Section 50
-Paragraph 1
-Subparagraph ((d)(5))
-URI http://asc.fasb.org/extlink&oid=121641442&loc=d3e19393-158473

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121639652&loc=d3e7104-158389

+ Details

Name:	us-gaap_NetAmountAtRiskByProductAndGuaranteeWeightedAverageAttainedAge1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_VariableAnnuityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GuaranteedInsuranceContractTypeOfBenefitAxis=us-gaap_GuaranteedMinimumDeathBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: