Shareholders' Equity - Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average number of common shares outstanding (in shares)	57.0	59.9
Director Plan and deferred stock units (in shares)	0.2	0.2
ESOP (in shares)	0.2	0.2
Common shares outstanding - basic (in shares)	57.4	60.3
Common and potential common shares outstanding - diluted (in shares)	58.1	61.2
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive effect of stock (in shares)	0.4	0.5
Stock options award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive effect of stock (in shares)	0.3	0.4