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Share-Based Payments - Performance Related Incentive Plan For Disruptive Growth Function - Additional Information (Detail) - Performance Share Unit [member]
pure in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Share based arrangement vesting requirements The units vest after 5 years provided a performance test is met  
Senior Management [member]    
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Share-based compensation number of shares issued 2.7 2.0
Executive Board [member]    
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Share-based compensation number of shares issued 0.1