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Risk Management Activities - Market Risk - Interest Rate - Narrative (Detail) - USD ($)
$ in Millions
Dec. 31, 2021
Apr. 15, 2021
Dec. 31, 2020
Disclosure of Financial Risk Management [line items]      
Borrowings $ 1,078.1   $ 1,526.9
Face amount of borrowings 1,200.0    
Interest bearing borrowings | LIBOR [Member]      
Disclosure of Financial Risk Management [line items]      
Borrowings 83.5   333.5
US$150 million revolving senior secured credit facility - new      
Disclosure of Financial Risk Management [line items]      
Borrowings 83.5   0.0
Face amount of borrowings 150.0    
US$150 million revolving senior secured credit facility - new | Revolving credit facility      
Disclosure of Financial Risk Management [line items]      
Face amount of borrowings   $ 150.0  
Sensitivity to BBSY interest rates | Interest bearing borrowings | Floating Interest Rate [member]      
Disclosure of Financial Risk Management [line items]      
Borrowings exposed to interest rate fluctuations 0.0   200.0
Sensitivity to interest rates | Interest bearing borrowings      
Disclosure of Financial Risk Management [line items]      
Borrowings exposed to interest rate fluctuations $ 83.5   $ 533.5