CONTINGENCIES, COMMITMENTS, AND GUARANTEES - SO Other Matters (Details) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2020 USD ($) leveraged_lease asset network heating_system	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) leveraged_lease	Dec. 31, 2020 USD ($) leveraged_lease asset network heating_system	Dec. 31, 2019 USD ($) leveraged_lease	Dec. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Number of leveraged leases	4		4	4	4
Number of domestic leveraged leases	2		2	2	2
Number of international leveraged leases	2		2	2	2
Lease, impairment loss | $	$ 52	$ 154	$ 17	$ 206	$ 0	$ 0
Lease, impairment loss, after tax | $	$ 31	$ 74	$ 13
Leveraged leases, number of gas distribution networks | network	9			9
Leveraged leases, number of district heating systems | heating_system	2			2
Leveraged leases, number of assets remaining | asset	10			10
Leveraged leases, purchase option, notice period				1 year