Stock-Based Compensation - Summary Of Changes In SARs Outstanding (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized, period for recognition	2 years 6 months
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Award expiration period from date of grant	7 years
Total compensation cost not yet recognized, period for recognition	4 years
SARs [Roll Forward]
Outstanding beginning balance (in shares)	1.2
Granted (in shares)	0.3
Forfeited (in shares)	(0.1)
Exercised (in shares)	(0.1)
Outstanding ending balance (in shares)	1.3	1.2
Vested and exercisable at ending balance (in shares)	0.7
Per Share Weighted Average Exercise Price [Roll Forward]
Outstanding at beginning balance (in dollars per share)	$ 89.45
Granted (in dollars per share)	143.23
Forfeited (in dollars per share)	118.31
Exercised (in dollars per share)	70.54
Outstanding at ending balance (in dollars per share)	100.54	$ 89.45
Vested and exercisable at ending balance (in dollars per share)	83.36
Per Share Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding beginning balance (in dollars per share)	19.88
Granted (in dollars per share)	32.62
Forfeited (in dollars per share)	26.52
Exercised (in dollars per share)	16.64
Outstanding ending balance (in dollars per share)	22.43	$ 19.88
Vested and exercisable ending balance (in dollars per share)	$ 18.46
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Remaining Contractual Term [Abstract]
Outstanding weighted average remaining contractual term	4 years 2 months 4 days	4 years 3 months 29 days
Granted	6 years 4 months 9 days
Vested and exercisable at ending balance	3 years 1 month 9 days
Aggregate Intrinsic value of outstanding shares	$ 56.9
Aggregate intrinsic value of shares vested and exercisable	$ 42.1
Unvested | Stock appreciation rights
SARs [Roll Forward]
Outstanding ending balance (in shares)	0.6