Summary of Significant Accounting Policies Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Income [Abstract]
Net income (loss)	$ (7.0)	$ 32.0	$ (16.6)	$ 58.4
Less: preferred stock dividend requirements	15.1	0.4	30.2	0.8
Earnings (loss) available for common shareholders	$ (22.1)	$ 31.6	$ (46.8)	$ 57.6
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)	215.5	154.6	215.4	154.5
Add: effect of dilutive securities (in shares)	0.0	0.2	0.0	0.4
Diluted average number of common shares outstanding (in shares)	215.5	154.8	215.4	154.9
Earnings Per Share [Abstract]
Basic and Diluted EPS	$ (0.10)	$ 0.20	$ (0.22)	$ 0.37
Series B Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage			7.00%		7.00%

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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 percentage rate used to calculate dividend payments on preferred stock.

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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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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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