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Contingencies and guarantees - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2018
USD ($)
Lawsuits
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Disclosure of contingent liabilities [line items]      
Outstanding letters of credit $ 29,000,000 $ 35,000,000  
Guarantees of loans made to equity accounted investments 43,000,000 54,000,000  
Other contingent liabilities 0 0  
Maximum [member]      
Disclosure of contingent liabilities [line items]      
Litigation settlement amount 2,000,000    
Performance guarantees [member]      
Disclosure of contingent liabilities [line items]      
Performance guarantees provided for in the financial statements 3,000,000 6,000,000  
Maximum unprovided exposure for guarantees 42,000,000 31,000,000  
Security Incidents [member]      
Disclosure of contingent liabilities [line items]      
Provision 0 $ 5,000,000 $ 5,000,000
Litigation settlement amount $ 3,000,000    
Number of lawsuits filed againsts group | Lawsuits 4    
Americas security incident [member]      
Disclosure of contingent liabilities [line items]      
Number of managed properties affected by security incident     12