Earnings Per Common Share (Calculations) (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share, Diluted [Abstract]
Weighted average common shares outstanding	249,800,000	257,600,000
Effect of dilutive securities:
Stock options	900,000	1,100,000
Other stock compensation plans	700,000	800,000
Potentially dilutive common shares	1,600,000	1,900,000
Adjusted weighted average common shares outstanding	251,400,000	259,500,000
Outstanding stock options excluded from the computation of diluted earnings per share due to their antidilutive effect	1,100,000.0	1,200,000.0