Mergers and Acquisitions (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Business Combinations [Abstract]
Integration and transaction-related costs, pre-tax	$ 112	$ 114	$ 339	$ 405
Integration and transaction-related costs, after-tax	$ 83	$ 88	$ 256	$ 311

After-tax transaction-related costs including the impact of tax benefits realized from termination of merger agreement. Transaction-related costs consist primarily of fees for legal, advisory and other professional services as well as employee costs.

No definition available.

Name:	ci_TransactionRelatedCostsAfterTax
Namespace Prefix:	ci_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration