Capital Stock (Par Value Of Stock) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Stockholders' Equity Note, Percent of Entity Owned by Current and Retired Employees	100.00%
Common Stock, Shares, Issued, Voting Trustees	18,665,064	17,754,923
Common stock stated value per share (USD per share)	$ 20.00	$ 20.00
Payments of Ordinary Dividends, Common Stock	$ 107.2	$ 46.9	$ 35.4
Common stock, subscriptions ( in shares)	997,275
Common shares subscribed (in dollars)	$ 19.9
Treasury Stock Transactions, Excluding Value of Shares Reissued [Abstract]
Shares of common stock purchased	962,023	786,754	684,347
Shares of common stock retired	957,495	752,825	678,958
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
Common stock dividend declared, percent	5.00%	10.00%	10.00%
2017 Voting Trust | Common Stock
Class of Stock [Line Items]
Percentage Ownership in Voting Trust	83.00%