SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Period for probable revenue recovery	24 months
Cash payments arising from operating leases	$ 848
ROU assets	2,662
Lease liabilities	$ 2,653
Weighted average remaining lease term	6 years 1 month 13 days
Weighted average discount rate	6.10%
Minimum
Lessee, Lease, Description [Line Items]
Power purchase agreement, term	5 years
Maximum
Lessee, Lease, Description [Line Items]
Power purchase agreement, term	20 years
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
ROU assets		$ 2,800
Lease liabilities		$ 2,800