Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2018	Sep. 30, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 105	$ 113
Common stock, par value per share	$ 0.50	$ 0.50
Common stock, shares authorized	1,200.0	1,200.0
Common stock, shares issued	953.4	953.4
Common stock, shares outstanding	615.8	629.2
Treasury stock, shares	337.5	324.2

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) 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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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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