Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Dilutive Impact of Common Stock Equivalents on Earnings per Share (Abstract]
Net income	$ 291	$ 239
Basic earnings per share [Abstract]
Earnings available to common shareholders	$ 291	$ 239
Weighted average common shares outstanding - basic (in shares)	509.0	508.3
Earnings available to common shareholders - basic (in dollars per share)	$ 0.57	$ 0.47
Effect of dilutive securities [Abstract]
Time based equity awards (in shares)	0.5	0.5
Diluted earnings per share [Abstract]
Earnings available to common shareholders	$ 291	$ 239
Weighted average common shares outstanding - diluted (in shares)	509.0	508.8
Earnings available to common shareholders - diluted (in dollars per share)	$ 0.57	$ 0.47

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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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 portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders.

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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.

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