Earnings Per Share and Shareholders' Equity Transactions (Narrative) (Details) - USD ($) shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Class Of Stock [Line Items]
Antidilutive securities excluded from calculation of earnings per share	0.5	0.6	0.5	0.5
Repurchases common stock, shares			0.4
Repurchases common stock, value			$ 37,200,000
Maximum [Member]
Class Of Stock [Line Items]
Repurchases common stock, authorized	$ 900,000,000		$ 900,000,000