Insurance and Contractholder Liabilities - Narrative (Details) - U.S. Medical - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Insurance and Contractholder Liabilities [Line Items]
Total of incurred but not reported liabilities plus expected claim development on reported claims, including reported claims in process	$ 3,000	$ 2,800
Favorable (unfavorable) impact of prior year development on shareholders' net income	30	68
Favorable (unfavorable) impact of prior year development on pre-tax income	$ 38	$ 86

Represents the total liability for incurred but not reported claims plus expected claim development on reported claims, including reported claims in process. Excludes amounts due for physician incentives and other medical care expenses and services payable.

No definition available.

Name:	ci_LiabilityForClaimsAndClaimsAdjustmentExpenseExcludingPhysicianIncentivesAndOtherExpenses
Namespace Prefix:	ci_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant