Capital Stock - Common Shares in Treasury and Common Shares Outstanding (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation Of Common Stock And Treasury Stock Balances [Roll Forward]
Balance (in shares)	93,116,762	93,883,645
Balance (in shares)	92,144,839	93,116,762	93,883,645
Shares in Treasury
Reconciliation Of Common Stock And Treasury Stock Balances [Roll Forward]
Balance (in shares)	25,255,036	23,676,733	23,577,411
Shares tendered as payment for option rights exercised (in shares)	3,838	1,159	16,545
Shares tendered in connection with vesting of restricted stock units (in shares)	55,095	52,144	82,777
Treasury stock purchased (in shares)	1,675,000	1,525,000
Shares transferred from defined benefit pension plan (in shares)	300,000
Balance (in shares)	27,288,969	25,255,036	23,676,733
Shares Outstanding
Reconciliation Of Common Stock And Treasury Stock Balances [Roll Forward]
Balance (in shares)	93,116,762	93,883,645	93,013,031
Shares tendered as payment for option rights exercised (in shares)	(3,838)	(1,159)	(16,545)
Shares issued for exercise of option rights (in shares)	901,878	661,599	969,936
Shares tendered in connection with vesting of restricted stock units (in shares)	(55,095)	(52,144)	(82,777)
Net shares issued for vesting of restricted stock units (in shares)	160,132	149,821
Treasury stock purchased (in shares)	1,675,000	1,525,000
Shares transferred from defined benefit pension plan (in shares)	300,000
Balance (in shares)	92,144,839	93,116,762	93,883,645