Quarterly report pursuant to Section 13 or 15(d)

Equity - Additional Information (Detail)

v3.7.0.1
Equity - Additional Information (Detail) - Restricted stock and restricted stock units [Member] - 2013 Plan [Member] - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Equity-based compensation expense $ 3 $ 3 $ 6 $ 5
Unrecognized compensation expense $ 17   $ 17  
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     2020