Share-Based Compensation Plans - RTSR fair value assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield			0.80%
Volatility, as a percent			31.20%
Risk-free interest rate			2.80%
Expected life in years			5 years 7 months 6 days
RTSR
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	1.60%	1.60%	0.90%
Volatility, as a percent	40.40%	40.20%	35.30%
Risk-free interest rate	0.60%	1.90%	2.40%
Expected life in years	2 years 9 months 18 days	2 years 4 months 24 days	2 years 9 months 18 days