Share-Based Compensation - Schedule of Stock Option Activity (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Shares Under Option
Outstanding at beginning of period	3,847
Exercised	(92)
Outstanding at end of period	3,755	3,847
Vested and expected to vest at end of period	3,745
Exercisable at end of period	1,729
Weighted Average Exercise Price
Outstanding at beginning of period	$ 19.43
Exercised	$ 13.21
Outstanding at end of period	$ 19.58	$ 19.43
Vested and expected to vest at end of period	$ 19.60
Exercisable at end of period	$ 10.48
Weighted Average Remaining Contractual Term (years)
Outstanding	4 years 4 months 24 days	4 years 8 months 12 days
Vested and expected to vest at end of period	4 years 4 months 24 days
Exercisable at end of period	5 years 2 months 12 days
Aggregate Intrinsic Value
Outstanding at beginning of period	$ 12.6
Outstanding at end of period	16.6	12.6
Vested and expected to vest at end of period	16.6
Exercisable at end of period	$ 15.1