Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock option exercises/deferred stock unit conversions, shares	399,224	548,238	1,150,920
Purchase of treasury stock, shares	716,062	1,037,982	1,149,555
Approximate cash dividends declared on preferred stock, per share	$ 1.34	$ 1.34	$ 1.34
Cash dividends - common stock, per share	$ 2.80	$ 2.58	$ 2.25