Reconciliation of Basic to Diluted Shares Outstanding (Detail) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule Of Earnings Per Share Basic And Diluted By Common Class [Line Items]
Basic	191.1	191.7	191.1	193.3
Dilutive effect of shares issuable under stock-based compensation plans	3.0	2.6	3.0	2.7
Diluted	194.1	194.3	194.1	196.0
Anti-dilutive options to purchase common shares and restricted stock as well as contingently issuable restricted stock which are excluded from the table above	0.5	0.5	0.6	0.9