GEOGRAPHIC AREAS - Long-Lived Assets by Geographic Area (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 14,998	$ 15,145	$ 16,433
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	14,778	14,922	15,700
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	220	223	206
Other foreign countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 0	$ 0	$ 527