Annual report pursuant to Section 13 and 15(d)

Equity - Summary of Equity-based Compensation Expense and Fair Value of Shares Vested on Vesting Date (Detail)

v3.8.0.1
Equity - Summary of Equity-based Compensation Expense and Fair Value of Shares Vested on Vesting Date (Detail) - Restricted Incentive [Member] - 2013 Plan [Member] - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Equity-based compensation expense $ 11 $ 10 $ 11
Fair value of awards vested on vesting date $ 5 $ 14 $ 6