Earnings Per Share and Shareholders' Equity Transactions (Narrative) (Details) - USD ($) shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Class Of Stock [Line Items]
Antidilutive securities excluded from calculation of earnings per share	0.3	1.0	0.3	0.9
Repurchases common stock, shares			0.2
Repurchases common stock, value			$ 25,300,000
Maximum [Member]
Class Of Stock [Line Items]
Repurchases common stock, authorized	$ 900,000,000		$ 900,000,000