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Financial Instruments - Summary of Fair Value of Liabilities Measurement Using Significant Unobservable Inputs (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of significant unobservable inputs used in fair value measurement of liabilities [line items]    
Opening balance $ 11,974.6 $ 11,719.8
Ending balance 11,293.3 11,974.6
Opening balance 7,797.1  
Ending balance 7,353.2 7,797.1
Level 3 [member]    
Disclosure of significant unobservable inputs used in fair value measurement of liabilities [line items]    
Opening balance 59.6 35.0
Adding Shares   58.8
Disposal Claim   (34.8)
Ending balance 59.9 59.6
Opening balance 108.9 122.2
Market value 16.5 (13.3)
Ending balance $ 125.4 $ 108.9