Income Per Common Share (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
Numerator (basic and diluted):
Income from continuing operations	$ 184	$ 170	$ 546	$ 517
Less: Allocation to unvested restricted stock awards	1	1	4	5
Income from continuing operations attributable to common shareholders	183	169	542	512
(Loss) income from discontinued operations, net	(58)	10	(64)	23
Less: Allocation to unvested restricted stock awards	0	0	0	0
(Loss) income from discontinued operations attributable to common shareholders	(58)	10	(64)	23
Net income available to common shareholders	$ 125	$ 179	$ 478	$ 535
Denominator:
Basic common shares (based upon weighted average) (in shares)	286	304	289	307
Add: Stock option dilution (in shares)	1	2	1	2
Diluted common shares (in shares)	287	306	290	309

Allocation To Unvested Restricted Stock Awards Discontinuing Operations

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

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Amount after tax of income (loss) from a discontinued operation attributable to the parent. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

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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; of income (loss) from continuing operations 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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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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