BASIS OF PRESENTATION AND SIGNIFICANT EVENTS Workforce Optimization (Details) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
	Feb. 16, 2017 USD ($)	Sep. 30, 2017 USD ($) employee $ / shares	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Oct. 31, 2017 employee
Business Acquisition [Line Items]
Transaction costs (break up fee received)		$ 0	$ 20	$ (947)	$ 81
Expected number of associates impacted | employee		2,700
Expected percentage of workforce associates impacted		5.70%
Estimated charges		$ 124
Estimated charges per diluted share (in USD per share) | $ / shares		$ 0.54
Subsequent Event
Business Acquisition [Line Items]
Entity number of employees | employee						47,200
Settled litigation | U.S. Department Of Justice vs. Humana and Aetna
Business Acquisition [Line Items]
Transaction costs (break up fee received)	$ 1,000