Earnings Per Common Share (Calculations) (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Diluted [Abstract]
Weighted average common shares outstanding	244,900,000	257,100,000	247,400,000	257,400,000
Effect of dilutive securities:
Stock options	800,000	1,100,000	800,000	1,100,000
Other stock compensation plans	700,000	800,000	700,000	800,000
Potentially dilutive common shares	1,500,000	1,900,000	1,500,000	1,900,000
Adjusted weighted average common shares outstanding	246,400,000	259,000,000	248,900,000	259,300,000
Outstanding stock options excluded from the computation of diluted earnings per share due to their antidilutive effect	1,100,000.0	600,000.0	1,100,000.0	600,000.0