Earnings Per Share and Shareholders' Equity Transactions (Narrative) (Details) - USD ($) shares in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Class Of Stock [Line Items]
Antidilutive securities excluded from calculation of earnings per share	0.5	0.3	0.5
Repurchases common stock, shares		0.4
Repurchases common stock, value		$ 44,200,000
Maximum [Member]
Class Of Stock [Line Items]
Repurchases common stock, authorized		$ 900,000,000

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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