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Share-Based Compensation - Additional Information (Detail)
12 Months Ended
Dec. 31, 2017
USD ($)
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Common stock, authorized shares 6,000,000,000
2017 Employee Plan [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Shares of common stock reserved for future issuance 6,554,307
Compensation expense | $ $ 15,000,000
Unrecognized compensation costs related to unvested awards | $ $ 19,000,000
Unrecognized compensation costs related to unvested awards, weighted-average period 1 year 7 months 6 days
2017 Employee Plan [Member] | Maximum [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Common stock, authorized shares 8,000,000
2017 Director Plan [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Shares of common stock reserved for future issuance 393,958
2017 Director Plan [Member] | Maximum [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Common stock, authorized shares 450,000
Performance Stock Units ("PSUs") [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Vesting rights zero to 200%
Performance Stock Units ("PSUs") [Member] | Maximum [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Share-based compensation arrangement by share-based payment award performance period 3 years
Vesting rights 200%
Performance Stock Units ("PSUs") [Member] | Minimum [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Share-based compensation arrangement by share-based payment award performance period 2 years
Market capitalization | $ $ 1,000,000,000
Vesting rights 0%