CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED BALANCE SHEETS
Trade accounts receivable, allowances (in dollars)	$ 122	$ 125
Convertible perpetual preference shares, par value (in dollars per share)	$ 0.01	$ 0.01
Convertible perpetual preference shares, authorized	6,900,000	6,900,000
Convertible perpetual preference shares, issued	6,900,000	6,900,000
Convertible perpetual preference shares, outstanding	6,900,000	6,900,000
Convertible perpetual preference shares, liquidation preference (in dollars per share)	$ 100	$ 100
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares, authorized	400,000,000	400,000,000
Common shares, issued	139,500,862	142,483,467
Common shares, outstanding	139,500,862	142,483,467
Treasury shares, at cost	12,882,313	9,586,083

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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-Publisher FASB
-Name Accounting Standards Codification
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Face amount or stated value per share of common stock.

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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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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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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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