Mergers and Acquisitions - Transaction-related Costs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Before-tax [Abstract]
Transaction-related costs, net	$ 155	$ 130	$ 291	$ 190
After-tax [Abstract]
Transaction-related costs, net - after-tax	$ 115	$ 109	$ 223	$ 159

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