Common and Preferred Stock - Share Activity of Old Cigna and Cigna (Details) - $ / shares		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 20, 2018	Dec. 31, 2017
Changes in Total Equity [Roll Forward]
Outstanding - beginning balance (in shares)		372,531,000	380,924,000	0	0
Exchange of Old Cigna shares for shares of Cigna (in shares)				243,785,000
Shares issued to Express Scripts shareholders (in shares)				137,337,000
Issued for stock option exercises and other benefit plans (in shares)		4,142,000	3,413,000	91,000
Repurchased common stock (in shares)		(21,902,000)	(11,806,000)	(289,000)
Outstanding - ending balance (in shares)	380,924,000	354,771,000	372,531,000	380,924,000
Treasury stock (in shares)	570,000	35,505,000	13,012,000	570,000
Issued (in shares)	381,494,000	390,276,000	385,543,000	381,494,000
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	600,000,000	600,000,000	600,000,000	600,000,000
Old Cigna
Changes in Total Equity [Roll Forward]
Outstanding - beginning balance (in shares)	243,785,000		0	243,967,000	243,967,000
Exchange of Old Cigna shares for shares of Cigna (in shares)	(243,785,000)
Issued for stock option exercises and other benefit plans (in shares)					1,118,000
Repurchased common stock (in shares)					(1,300,000)
Retirement of treasury stock (in shares)	(52,358,000)
Exchange of Old Cigna certificated treasury stock for new Cigna certificated treasury stock (in shares)	(2,000)
Outstanding - ending balance (in shares)	0			0	243,785,000
Treasury stock (in shares)	0			0
Issued (in shares)	0			0
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock, par value (in dollars per share)						$ 0.25
Common stock, shares authorized (in shares)						600,000,000