Net Income Per Share NeNet Income Per Share (Schedule of Weighted Average Number of Shares) (Details) - shares shares in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Basic weighted average shares outstanding	169	170
Dilution attributable to stock-based compensation awards	0	1
Diluted weighted average shares outstanding	169	171

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- Definition

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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
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- Definition

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.

+ References

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 260
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