Summary of Significant Accounting Policies, Net Income per Share (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Income Per Share [Abstract]
Potential shares attributable to exercises included in diluted EPS calculation (in shares)	0.1	0.7	0.9
Shares excluded from diluted EPS calculation (in shares)	0.2	0.0	0.0