Summary of Significant Accounting Policies - EPS and New Accounting Principle (Details) - shares shares in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings per share
Basic weighted average number of shares outstanding	307,781	317,082	308,509	316,850
Diluted weighted average number of shares outstanding	307,781	317,082	308,646	316,850
Restricted stock and restricted stock unit
Earnings per share
Add: Dilutive effect of non-vested restricted stock units			27
Weighted Average Anti-dilutive Awards	2,356	2,813	2,008	2,996
Stock options
Earnings per share
Weighted Average Anti-dilutive Awards	514	619	541	637
Performance share unit awards
Earnings per share
Add: Dilutive effect of non-vested restricted stock units			110
Weighted Average Anti-dilutive Awards	2,676	1,880	2,141	1,665

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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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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