Capital Stock (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Percent of stock owned by active and retired employees	100.00%
Common stock, stated value per share	$ 20.00	$ 20.00
Cash dividends	$ 80.4	$ 92.8	$ 137.2
Common stock, subscriptions ( in shares)	1,347,781
Common shares subscribed (in dollars)	$ 27.0
Preferred stock shares authorized	10,000,000	10,000,000
Preferred stock par or stated value per share (USD per share)	$ 0.01	$ 0.01
Preferred stock outstanding (in shares)	0	0
2017 Voting Trust [Member] | Common Stock [Member]
Class of Stock [Line Items]
Percent of shares held in voting trust	83.00%