Share-Based Compensation - Aggregate Intrinsic Value and Closing Stock Price of Options (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Payment Arrangement [Abstract]
Closing stock price (usd per share)	$ 215.53		$ 215.53
Total intrinsic value of options exercised	$ 3.3	$ 6.9	$ 11.6	$ 14.4

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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Balance Type:	debit
Period Type:	duration