Capital Stock (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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 dvidends	$ 90.7	$ 107.2	$ 46.9
Common stock, subscriptions ( in shares)	1,052,817
Common shares subscribed (in dollars)	$ 21.1
Common stock dividend declared, percent		5.00%	10.00%
Treasury Stock Transactions, Excluding Value of Shares Reissued [Abstract]
Shares of common stock purchased	824,685	962,023	786,754
Shares of common stock retired	830,338	957,495	752,825
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 | Common Stock
Class of Stock [Line Items]
Percent of shares held in voting trust	83.00%