Stock-based Compensation Plans (Summary of Stock Option Plan Activity) (Parenthetical) (Details) - $ / shares		1 Months Ended	12 Months Ended
		Jan. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options related to special dividends paid		67,605		67,605
Remaining option awards granted			185,208
Granted, Weighted Average Exercise Price	[1]		$ 118.34	$ 119.36	$ 110.98

[1] In accordance with plan provisions, 2019 includes 67,605 options related to special dividends paid by the Company in January 2019 and December 2019, in order to retain the intrinsic value of outstanding awards. The remaining 185,208 option awards were granted at an exercise price of $119.36.