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Share-Based Compensation - Additional Information (Detail) - EUR (€)
€ in Millions
6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Share Based Payment Plans [line items]    
Total expense related to the potential ordinary shares € 7 € 6
Performance share units (PSUs) [member]    
Share Based Payment Plans [line items]    
Share based compensation, vesting period 3 years  
Percentage of vesting multiplier 100.00%  
PSUs granted in 2015 and 2016 [member] | Bottom of range [member]    
Share Based Payment Plans [line items]    
Percentage of vesting multiplier 0.00%  
PSUs granted in 2015 and 2016 [member] | Top of range [member]    
Share Based Payment Plans [line items]    
Percentage of vesting multiplier 200.00%