Document and Entity Information - $ / shares	9 Months Ended
	Sep. 30, 2018	Oct. 19, 2018	Dec. 31, 2017
Document Document And Entity Information [Abstract]
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Entity Registrant Name	CIGNA Corporation
Entity Central Index Key	0000701221
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Trading Symbol	CI
Entity Common Stock Shares Outstanding		243,534,265
Amendment Flag	false
Entity Current Reporting Status	Yes
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Common stock, par value per share	$ 0.25		$ 0.25