Share-Based Compensation Plans - Terms and Assumptions (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
TSR PSU
Weighted-average assumptions used to estimate fair value:
Expected dividend yield	0.70%	0.80%	0.80%
Expected stock price volatility	29.60%	30.80%	29.90%
Risk-free interest rate	1.40%	2.50%	2.40%
Contractual term in years	2 years 10 months 24 days	2 years 9 months 18 days	2 years 10 months 24 days
Weighted-average fair value estimate at grant date	$ 3.6	$ 3.0	$ 3.2
Weighted-average fair value estimate per share (in dollars per share)	$ 94.53	$ 105.16	$ 79.05
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%
Expected stock price volatility			29.30%
Risk-free interest rate			2.60%
Contractual term in years	4 years 6 months		4 years 6 months
Market price (in dollars per share)	$ 72.00
Weighted-average fair value estimate at grant date			$ 7.0
Weighted-average fair value estimate per share (in dollars per share)	$ 0		$ 16.73
Time Based Vesting Option
Weighted-average assumptions used to estimate fair value:
Expected dividend yield	0.70%	0.80%
Expected stock price volatility	29.70%	30.30%
Risk-free interest rate	1.30%	2.50%
Contractual term in years	4 years 6 months	4 years 6 months
Market price (in dollars per share)	$ 72.00
Weighted-average fair value estimate at grant date	$ 1.7	$ 3.0
Weighted-average fair value estimate per share (in dollars per share)	$ 21.10	$ 21.58