Earnings Per Common Share (Calculations) (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Diluted [Abstract]
Weighted average common shares outstanding	242,200,000	256,400,000	245,800,000	257,000,000
Effect of dilutive securities:
Stock options	700,000	1,000,000	800,000	1,000,000
Other stock compensation plans	700,000	800,000	700,000	800,000
Potentially dilutive common shares	1,400,000	1,800,000	1,500,000	1,800,000
Adjusted weighted average common shares outstanding	243,600,000	258,200,000	247,300,000	258,800,000
Outstanding stock options excluded from the computation of diluted earnings per share due to their antidilutive effect	1,000,000	500,000.0	1,000,000.0	600,000.0