Stockholders' Equity - Statement of Changes in Common Shares Outstanding (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class A Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Purchases of treasury stock	(16.5)	(14.3)	(26.4)
Common Stock | Class A Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	986.9	996.0	1,018.6
Purchases of treasury stock	(16.5)	(14.3)	(26.4)
Share-based payments	1.2	2.3	3.2
Conversion of Class B to Class A common stock	0.5	2.9	0.6
Balance	972.1	986.9	996.0
Common Stock | Class B Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	8.3	11.2	11.8
Conversion of Class B to Class A common stock	(0.5)	(2.9)	(0.6)
Balance	7.8	8.3	11.2