Capital Stock (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Total Shares Authorized	210,000,000
Preferred Stock, Shares Authorized	10,000,000	10,000,000
Preferred Stock, Par Value	$ 0.01	$ 0.01
Phantom Stock Value Per Share	$ 3.33
SERP units	28,950	38,754	47,487
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 925.0
Common Stock, Voting Rights	one vote per share
Class A [Member]
Class Of Stock [Line Items]
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Par Value	$ 0.01	$ 0.01
Class B [Member]
Class Of Stock [Line Items]
Common Stock, Shares Authorized	0	0
Common Stock, Par Value	$ 0	$ 0