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FINANCIAL RISK MANAGEMENT FINANCIAL RISK MANAGEMENT - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Disclosure of detailed information about borrowings [line items]    
Letter of credit outstanding amount $ 54,000,000 $ 47,000,000
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Financial assets 3,982,000,000 3,056,000,000
Market risk    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Impact of 10% change in value of investments on Equity 14,000,000  
Impact of 10 Percent Change in Value of Investments on Profit Loss 7,000,000  
Impact of 10% change in value of investments on Comprehensive Income 7,000,000  
Marketable securities    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Financial assets 142,000,000 173,000,000
Marketable securities | Market risk    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Financial assets 142,000,000 173,000,000
Corporate revolving credit facility    
Disclosure of detailed information about borrowings [line items]    
Credit facility, maximum borrowing capacity 1,975,000,000.000  
Non-recourse borrowings 820,000,000 510,000,000
Letter of credit outstanding amount 54,000,000 47,000,000
Credit facility    
Disclosure of detailed information about borrowings [line items]    
Credit facility, maximum borrowing capacity 500,000,000  
Non-recourse borrowings $ 0 $ 0