Earnings Per Share - Reconciliation of the Numerators and Denominators of the Earnings Per Share Calculations (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income available to common stockholders - Numerator diluted	$ 111	$ 95	$ 141	$ 327
Net income available to common stockholders - Numerator basic	$ 111	$ 95	$ 141	$ 327
Weighted-average common shares outstanding - Basic	144.0	144.7	144.0	145.1
Employee compensation-related shares, including stock options	0.8	1.2	0.8	1.5
Weighted-average common shares outstanding - Diluted	144.8	145.9	144.8	146.6

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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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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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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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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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