Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 66	$ 63
Allowance for doubtful notes receivable	$ 4	$ 4
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	1,000,000,000us-gaap_CommonStockSharesAuthorized	1,000,000,000us-gaap_CommonStockSharesAuthorized
Common stock, outstanding	171,808,011us-gaap_CommonStockSharesOutstanding	172,694,299us-gaap_CommonStockSharesOutstanding

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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A valuation allowance relating to a written agreement to receive money (at a specified future date(s) within one year from the reporting date (or the normal operating cycle, whichever is longer), consisting of principal as well as any accrued interest) for the portion that is 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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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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