SUPPLEMENTARY INFORMATION - Equity Method Investments (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity method investment	$ 190	$ 188
Equity method investment, consideration receivable	17	27
Shareholder loan	$ 34	$ 29
Dublin
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent	50.00%	50.00%
Equity method investment	$ 145	$ 153
Ambiente 2000 S.r.l.
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent	40.00%	40.00%
Equity method investment	$ 1	$ 0
Earls Gate
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent	25.00%	25.00%
Equity method investment	$ 10	$ 9
Shareholder loan	$ 16	$ 16
Rookery
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent	40.00%	40.00%
Equity method investment	$ 10	$ 4
Equity method investment, consideration receivable	$ 13	$ 17
Newhurst Energy Recovery Facility
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent	25.00%	25.00%
Equity method investment	$ 14	$ 9
Equity method investment, consideration receivable	4	4
Shareholder loan	$ 5	$ 3
Protos
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent	37.50%	37.50%
Equity method investment	$ 3	$ 6
Equity method investment, consideration receivable	0	6
Shareholder loan	$ 4	$ 1
Zhao County Investment
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent	26.00%	26.00%
Equity method investment	$ 7	$ 7
Shareholder loan	$ 9	$ 9