Summary of Significant Accounting Policies Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Accounting Policies [Abstract]
Net income (loss)	$ 23.8	$ 26.0
Income [Abstract]
Less: preferred stock dividend requirements	0.4	0.4
Earnings (loss) available for common shareholders	$ 23.4	$ 25.6
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)	153.7	153.4
Add: effect of dilutive securities (in shares)	0.3	0.3
Diluted average number of common shares outstanding (in shares)	154.0	153.7
Earnings Per Share [Abstract]
Earnings Per Share, Basic and Diluted	$ 0.15	$ 0.17

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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The amount of preferred stock dividends that is an adjustment to net income apportioned to common stockholders.

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