BASIS OF PREPARATION AND SIGNIFICANT ACCOUNTING POLICIES - Revenue and expense recognition (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Derivatives
Disclosure of disaggregation of revenue from contracts with customers [line items]
Net realized gain (losses) on investments during the period	$ 15	$ (21)
Renewable Credits \| Goods or services transferred at point in time
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from contracts with customers	$ 25	$ 17

The amount of revenue from contracts with customers. A customer is a party that has contracted with an entity to obtain goods or services that are an output of the entity’s ordinary activities in exchange for consideration. [Refer: Revenue]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2018-01-01
-Paragraph 113
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_113_a&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2018-01-01
-Paragraph 114
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_114&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_RevenueFromContractsWithCustomers
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration