Earnings Per Common Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Numerator (basic and diluted):
Net income	$ 149	$ 138
Less: Allocation to unvested restricted stock awards	1	1
Net income available to common shareholders	$ 148	$ 137
Denominator:
Basic common shares (based upon weighted average) (in shares)	310	317
Add: Stock option dilution (in shares)	3	4
Diluted common shares (in shares)	313	321

Amount after tax of income (loss) from continuing operations attributable to the parent.

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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 of undistributed earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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