Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 1	$ 1
Variable interest entities - assets	241	240
Variable interest entities - liabilities	$ 216	$ 217
Common stock, par value (per share)	$ 0.01	$ 0.01
Common stock, authorized shares	6,000,000,000	6,000,000,000
Common stock, issued shares	201,253,015	214,873,778
Common stock, outstanding shares	201,178,717	214,845,244

For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

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The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

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