Stock-Based Compensation - Restricted Stock and RSU Activity (Parenthetical) (Detail) shares in Millions |
6 Months Ended | ||
|---|---|---|---|
|
Jun. 30, 2017
Tranche
shares
|
Jun. 30, 2016 |
Jun. 30, 2015 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share-based compensation awards expected to vest | 2.4 | ||
| Awards vested, not converted | 0.3 | ||
| Market Performance-Based RSUs [Member] | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share-based compensation awards expected to vest | 0.2 | ||
| Share price appreciation targets | 15.00% | 25.00% | 35.00% |
| Restricted stock units vesting period, years | 6 years | 6 years | 6 years |
| Number of tranches | Tranche | 3 | ||