SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Health Care Cost Payments, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Health care cost payments	$ (6,943)	$ (6,253)	$ (6,475)
Health care cost reimbursements	6,898	6,252	6,412
Net payments	$ (45)	$ (1)	$ (63)