Earnings Per Share, Share Repurchases and Dividends on Common Stock (Unaudited) (Details 2) - $ / shares shares in Millions	1 Months Ended			3 Months Ended
	Jan. 31, 2018	May 31, 2017	May 31, 2016	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Dilutive effect of of stock awards and options granted to employees under stock-based compensation plans				1.1	1.3
Common stock dividends per share, declared (in dollars per share)	$ 1.10	$ 1.00	$ 0.90	$ 1.10	$ 0.90
Increase in quarterly common stock dividend (percent)	10.00%	11.00%