Share-Based Compensation Plans - Terms and Assumptions (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
TSR PSU
Weighted-average assumptions used to estimate fair value:
Expected dividend yield	0.80%	0.80%	1.40%
Expected stock price volatility	29.90%	30.60%	29.10%
Risk-free interest rate	2.40%	1.40%	0.80%
Contractual term in years	2 years 10 months 24 days	2 years 10 months 24 days	2 years 8 months 12 days
Weighted-average fair value estimate at grant date	$ 3.2	$ 2.0	$ 2.3
Weighted-average fair value estimate per share (in dollars per share)	$ 79.05	$ 67.81	$ 31.64
Performance-based Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period for achieving stock price hurdles	3 years
Weighted-average assumptions used to estimate fair value:
Expected dividend yield	0.80%	0.80%	1.30%
Expected stock price volatility	29.30%	29.30%	30.90%
Risk-free interest rate	2.60%	1.80%	1.10%
Contractual term in years	4 years 6 months	4 years 6 months	4 years 6 months
Market price (in dollars per share)	$ 64.65
Weighted-average fair value estimate at grant date	$ 7.0	$ 3.6	$ 3.5
Weighted-average fair value estimate per share (in dollars per share)	$ 16.73	$ 11.97	$ 6.01
Time Based Vesting Option
Weighted-average assumptions used to estimate fair value:
Expected dividend yield		0.70%
Expected stock price volatility		28.90%
Risk-free interest rate		1.70%
Contractual term in years		4 years 6 months
Market price (in dollars per share)	$ 64.65
Weighted-average fair value estimate at grant date		$ 0.1
Weighted-average fair value estimate per share (in dollars per share)		$ 21.09