Weighted Average Shares Outstanding - Reconciliation of Basic to Diluted Shares Outstanding (Detail) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Basic (in shares)	187.7	189.4	187.6	189.9
Dilutive effect of shares issuable under stock-based compensation plans (in shares)	1.3	1.9	1.7	2.2
Diluted (in shares)	189.0	191.3	189.3	192.1
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	0.3	0.3	0.3