GOODWILL AND OTHER INTANGIBLE ASSETS - Changes in Carrying Amount of Goodwill by Reportable Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Beginning balance	$ 3,928	$ 3,897
Acquisitions	519	31
Ending balance	4,447	3,928
Retail
Goodwill [Roll Forward]
Beginning balance	1,535	1,535
Acquisitions	0	0
Ending balance	1,535	1,535
Group and Specialty
Goodwill [Roll Forward]
Beginning balance	261	261
Acquisitions	0	0
Ending balance	261	261
Healthcare Services
Goodwill [Roll Forward]
Beginning balance	2,132	2,101
Acquisitions	519	31
Ending balance	$ 2,651	$ 2,132