Stock-Based Compensation Plans - RSUs (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Additional share-based compensation disclosures
Total unrecognized compensation cost			$ 52.9
Weighted average recognition period for unrecognized compensation cost (in years)			1 year 4 months 24 days
RSUs, 2019 grant
Shares
Awards granted (in shares)			488,345
The number of grants made during the period on the basis of service and performance criteria other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).			194,155
Fair value of restricted stock granted (in dollars per share)			$ 88.05
Share of common stock			1
Changes
Granted (in shares)			488,345
Weighted Average Grant Date Fair Value
Granted (in dollars per share)			$ 88.05
RSUs, 2018 grant
Shares
Awards granted (in shares)				474,715
The number of grants made during the period on the basis of service and performance criteria other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).				178,970
Fair value of restricted stock granted (in dollars per share)				$ 84.26
Share of common stock				1
Changes
Granted (in shares)				474,715
Weighted Average Grant Date Fair Value
Granted (in dollars per share)				$ 84.26
RSUs, 2017 grant
Shares
Awards granted (in shares)					446,525
The number of grants made during the period on the basis of service and performance criteria other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).					169,009
Fair value of restricted stock granted (in dollars per share)					$ 79.60
Share of common stock					1
Changes
Granted (in shares)					446,525
Weighted Average Grant Date Fair Value
Granted (in dollars per share)					$ 79.60
Unvested RSUs
Shares
Awards granted (in shares)			488,345
Fair value of restricted stock granted (in dollars per share)			$ 88.05
Changes
Unvested at the beginning of the year (in shares)		859,005	889,830
Granted (in shares)			488,345
Vested (in shares)			(476,634)
Cancelled or forfeited (in shares)			(42,536)
Unvested at the end of the year (in shares)			859,005	889,830
Weighted Average Grant Date Fair Value
Unvested at the beginning of the year (in dollars per share)		$ 86.40	$ 82.05
Granted (in dollars per share)			88.05
Vested (in dollars per share)			80.18
Cancelled or forfeited (in dollars per share)			83.97
Unvested at the end of the year (in dollars per share)			$ 86.40	$ 82.05
Additional share-based compensation disclosures
Fair value of vested units			$ 56.5	$ 34.6	$ 40.1
Restricted stock
Shares
Payments to tax authorities on employees' behalf for shares withheld related to share settlements			$ 16.2	$ 12.3	$ 9.3
Performance-based | RSU's
Shares
Performance target period (in years)	3 years	3 years	3 years
Directors Equity Plan | Stock Awards
Shares
Awards granted (in shares)			11,640	13,880	18,120
Fair value of restricted stock granted (in dollars per share)			$ 89.34	$ 93.65	$ 71.73
Changes
Granted (in shares)			11,640	13,880	18,120
Weighted Average Grant Date Fair Value
Granted (in dollars per share)			$ 89.34	$ 93.65	$ 71.73