GEOGRAPHIC AREAS - Long-Lived Assets by Geographic Area (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 14,221	$ 14,349
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	13,922	14,074
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 299	$ 275