Weighted Average Shares Outstanding - Reconciliation of Basic to Diluted Shares Outstanding (Detail) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Basic (in shares)	186.7	187.7	187.0	187.6
Dilutive effect of shares issuable under stock-based compensation plans (in shares)	1.2	1.3	1.2	1.7
Diluted (in shares)	187.9	189.0	188.2	189.3
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)	0.2	0.3	0.3	0.3