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FINANCIAL RISK MANAGEMENT FINANCIAL RISK MANAGEMENT - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of detailed information about borrowings [line items]    
Letter of credit outstanding amount $ 47,000,000 $ 106,000,000
Financial assets 3,056,000,000 2,134,000,000
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 510,000,000 789,000,000
Credit facility    
Disclosure of detailed information about borrowings [line items]    
Credit facility, maximum borrowing capacity 500,000,000  
Non-recourse borrowings 0 0
Marketable securities    
Disclosure of detailed information about borrowings [line items]    
Financial assets 173,000,000 $ 85,000,000
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 17,000,000  
Impact of 10 Percent Change in Value of Investments on Profit Loss 13,000,000  
Impact of 10% change in value of investments on Comprehensive Income $ 4,000,000