Earnings Per Share - Number of Shares Underlying Stock Options Excluded from Computation of Diluted Loss (Detail) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options	0.3	0.7	0.4
Average exercise price	$ 42.43	$ 38.34	$ 42.50
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options	0.1	0.1	0.1
Minimum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Year(s) of expiration	2024	2024	2024
Maximum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Year(s) of expiration	2025	2026	2025