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FINANCIAL RISK MANAGEMENT FINANCIAL RISK MANAGEMENT - Additional Information (Details) - USD ($)
 2 Months Ended 12 Months Ended
Mar. 13, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about borrowings [line items]      
Financial assets   $ 2,134,000,000 $ 2,412,000,000
Subsidiary and corporate borrowings   10,164,000,000 8,326,000,000
Letter of credit outstanding amount   106,000,000 46,000,000
Credit facility      
Disclosure of detailed information about borrowings [line items]      
Credit facility, maximum borrowing capacity   500,000,000  
Subsidiary and corporate borrowings   0 0
Corporate revolving credit facility      
Disclosure of detailed information about borrowings [line items]      
Credit facility, maximum borrowing capacity   1,975,000,000.000  
Subsidiary and corporate borrowings   789,000,000 0
Letter of credit outstanding amount   106,000,000 46,000,000
Marketable securities      
Disclosure of detailed information about borrowings [line items]      
Financial assets   85,000,000 $ 3,000,000
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   9,000,000  
Impact of 10% change in value of investments on Comprehensive Income   $ 9,000,000  
Subsequent Event      
Disclosure of detailed information about borrowings [line items]      
Cancellation of letters of credit $ 59,000,000    
Subsequent Event | Credit facility      
Disclosure of detailed information about borrowings [line items]      
Subsidiary and corporate borrowings $ 400,000,000