Shareholders' Equity (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 01, 2022	Oct. 28, 2021	Dec. 31, 2020	Aug. 06, 2020	Dec. 31, 2007
Class of Stock [Line Items]
Shares registered	400,000,000			400,000,000	3,400,000
Class A Common Stock [Member] | November 16, 2007 Registration Statement [Member]
Class of Stock [Line Items]
Shares registered						4,000,000.0
Shares reclassified as authorized and unissued	1,200,000
Class A Common Stock [Member] | March 5, 2018 Registration Statement [Member]
Class of Stock [Line Items]
Securities issued	0			0
2020 Plan [Member]
Class of Stock [Line Items]
Shares registered					3,000,000.0
2010 Plan [Member]
Class of Stock [Line Items]
Shares registered					400,000
New Plan [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Stock repurchase program, remaining authorization		$ 586.4
New Plan [Member] | Class A Common Stock [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized			$ 1,000.0
Prior Plan [Member] | Class A Common Stock [Member]
Class of Stock [Line Items]
Stock repurchase program, remaining authorization			$ 125.1