Weighted Average Shares Outstanding - Reconciliation of Basic to Diluted Shares Outstanding (Detail) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Basic (in shares)	187.8	189.0	187.6	189.6
Dilutive effect of shares issuable under stock-based compensation plans (in shares)	1.5	2.1	1.7	2.2
Diluted (in shares)	189.3	191.1	189.3	191.8
Anti-dilutive options to purchase common shares and restricted stock as well as contingently issuable restricted stock which are excluded from the table above (in shares)	0.3	0.2	0.3	0.3