Earnings Per Share, Share Repurchases and Dividends on Common Stock (Unaudited) (Details 2) - $ / shares shares in Millions	1 Months Ended				3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jan. 31, 2018	May 31, 2017	May 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Dilutive effect of of stock awards and options granted to employees under stock-based compensation plans					0.9	1.0	1.0	1.1
Common stock dividends per share, declared (in dollars per share)	$ 1.20	$ 1.10	$ 1.00	$ 0.90			$ 2.30	$ 1.90
Increase in quarterly common stock dividend (percent)	9.00%	10.00%	11.00%