Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Millions	Dec. 31, 2021	Dec. 31, 2020
Common stock, shares, outstanding	114.0	113.3
Preferred Stock [Member]
Preferred stock, par or stated value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	10.0	10.0
Preferred stock, shares outstanding	0.0	0.0
Series Common Stock [Member]
Common stock, par or stated value per share	$ 0.01	$ 0.01
Common stock, shares authorized	40.0	40.0
Common stock, shares, outstanding	0.0	0.0
Common Stock [Member]
Common stock, par or stated value per share	$ 0.01	$ 0.01
Common stock, shares authorized	150.0	150.0
Common stock, shares issued	122.5	121.3
Treasury stock, shares	8.5	8.0