Earnings Per Share (Excluded from Diluted Earnings Per Share Calculation) (Details) - $ / shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted-average number of shares	0.2	0.0	0.2	0.2
Price range per share (in dollars per share)	$ 205.53	$ 0.00	$ 205.53	$ 156.94
Minimum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Price range per share (in dollars per share)		0.00		156.94
Maximum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Price range per share (in dollars per share)		$ 0.00		$ 156.94