Quarterly report pursuant to Section 13 or 15(d)

Equity - Additional Information (Detail)

v3.8.0.1
Equity - Additional Information (Detail) - Restricted stock and restricted stock units [Member] - 2013 Plan [Member] - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Equity-based compensation expense $ 3 $ 3 $ 8 $ 7
Unrecognized compensation expense $ 15   $ 15  
Weighted-average term in which unrecognized compensation expense is expected to be recognized     2 years  
Employees and Directors [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares awarded     707,648  
Employees and Directors [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted common shares vesting years     2017  
Employees and Directors [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted common shares vesting years     2021