Mergers and Acquistions - Merger Consideration (Details) $ / shares in Units, $ in Millions, $ in Millions	Dec. 31, 2018 USD ($) shares	Nov. 30, 2018 NZD ($)	Nov. 30, 2018 USD ($)	Dec. 20, 2018 $ / shares shares	Dec. 31, 2017 shares	Dec. 31, 2016 shares
Merger consideration [Abstract]
Common shares outstanding	380,924,000				0	0
Common Stock Shares Outstanding	380,924,000				0	0
Express Scripts Holding Company [Member]
Merger consideration [Abstract]
Common shares outstanding				564,300,000
Cash consideration per share | $ / shares				$ 48.75
Cash consideration paid to Express Scripts common stockholders | $	$ 27,510
Cash consideration paid in lieu of fractional shares | $	4
Cash consideration paid to Express Scripts performance share holders | $	65
Total cash consideration | $	$ 27,579
Common Stock Shares Outstanding				564,300,000
Per share exchange ratio				0.2434
Shares of Cigna issued to Express Scripts common stockholders	137,300,000
Shares of Cigna issued to Express Scripts performance share holders and other equity holders	300,000
Shares of Cigna issued to Express Scripts shareholders	137,600,000
Closing price of Cigna common stock | $ / shares				$ 179.8
Total stock consideration | $	$ 24,745
Noncontrolling interest | $	7
Fair value of other share-based compensation awards | $	479
Total merger consideration | $	$ 52,810
Number of Cigna stock options or restricted stock units awarded to holder of acquiree stock options and restricted stock units				0.4802
Expected life of acquiree stock option awards	4 years 3 months 18 days
OnePath Insurance [Member]
Merger consideration [Abstract]
Total cash consideration		$ 700	$ 480