Earnings Per Share - Computation of Basic and Diluted Earnings Per Share for Continuing Operations (Parenthetical) (Detail) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dilutive Securities Included And Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive impact of potential shares average share price			$ 9.62
Dilutive impact of potential shares conversion price			$ 7.41
Stock Compensation Plan [Member]
Dilutive Securities Included And Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Share based awards excluded from the calculation of diluted earnings per share	0.5	0.8	1.5