FAIR VALUE MEASUREMENTS - Book Values and Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Book values
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Short-term debt	$ 301	$ 0
Current maturities of long-term debt and finance lease obligations	209	406
Long-term debt and finance lease obligations	5,446	5,786
Fair values
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Short-term debt	301	0
Current maturities of long-term debt and finance lease obligations	213	409
Long-term debt and finance lease obligations	$ 5,950	$ 6,471