Condensed Balance Sheets Parenthetical - USD ($) shares in Millions, $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Assets
Accumulated depreciation	$ 3,997.2	$ 3,719.8	$ 3,602.4
Shareholders' equity:
Common stock, par value	$ 1.00	$ 1.00	$ 1.00
Common stock, authorized (in shares)	240.0	240.0	240.0
Common stock, issued	159.4	158.0	157.9
Common stock, outstanding	159.4	158.0	157.9

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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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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