Stockholders' Equity Scheduled Vesting for Outstanding Restricted Stock Units (Detail) - Restricted Stock Units shares in Millions	Sep. 30, 2015 shares
Schedule of Vesting [Line Items]
Three Months Ended December 31, 2015	1.8
Year Ended December 31, 2016	6.5
Year Ended December 31, 2017	6.9
Year Ended December 31, 2018	3.3
Year Ended December 31, 2019	1.3
Thereafter	0.3
Total	20.1