Condensed Consolidated Balance Sheets Parenthetical (USD $) In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Stockholders' Equity:
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	100.0us-gaap_PreferredStockSharesAuthorized	100.0us-gaap_PreferredStockSharesAuthorized
Preferred Stock, Shares Issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred Stock, Shares Outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	500.0us-gaap_CommonStockSharesAuthorized	500.0us-gaap_CommonStockSharesAuthorized
Common Stock, Shares, Issued	169.5us-gaap_CommonStockSharesIssued	168.6us-gaap_CommonStockSharesIssued
Common Stock, Shares, Outstanding	169.5us-gaap_CommonStockSharesOutstanding	168.6us-gaap_CommonStockSharesOutstanding

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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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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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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