Goodwill and Other Intangible Assets, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill, impaired, accumulated impairment loss	$ 860.0
Amortization expense	352.0	$ 223.0	$ 76.5
Live [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill, impaired, accumulated impairment loss	425.0
Learn [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill, impaired, accumulated impairment loss	$ 435.0