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Earnings (Loss) Per Share (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Earnings Per Share [Abstract]

Net income (loss)

$ (65.0)

$ (20.3)

$ 19.4

$ (0.3)

$ 35.8

$ 20.8

$ 7.1

$ (15.1)

$ (66.2)

$ 48.6

^[1],[2]

$ (252.4)

^[1]

Percentage allocated to common shareholders

100.00%

92.00%

100.00%

Basic and Diluted EPS:

Net income (loss) available to common stockholders, basic and diluted

$ (66.2)

$ (252.4)

Shares outstanding, basic and diluted (in shares)

87.6

87.1

Basic and diluted (in dollars per share)

$ (0.76)

$ (2.90)

EPS:

Net income allocated to common stockholders, basic

$ (65.0)

$ (20.3)

$ 17.9

$ (0.3)

$ 33.0

$ 19.1

$ 6.6

$ (15.1)

$ 44.7

Shares outstanding, basic (in shares)

87.3

Basic (in dollars per share)

$ (0.74)

$ (0.23)

$ 0.20

$ 0.00

$ 0.38

$ 0.22

$ 0.08

$ (0.17)

(0.76)

$ 0.51

^[2]

(2.90)

Dilutive effect of share-based payment arrangements

0.7

Net income (loss) available to common stockholders, diluted

$ 44.7

Shares outstanding, diluted (in shares)

88.0

Diluted (in dollars per share)

$ (0.74)

$ (0.23)

$ 0.20

$ 0.00

$ 0.37

$ 0.22

$ 0.07

$ (0.17)

$ (0.76)

$ 0.51

^[2]

$ (2.90)

[1]	As adjusted due to the adoption of ASU 2016-18 "Statement of Cash Flows (Topic 230) Restricted Cash."
[2]	As adjusted due to the adoption of ASU 2017-07 Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost

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