Revision of Previously Reported Financial Statements - Changes in Stockholders' Equity (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Balance, beginning of period	$ 303.8	$ 381.4
Other comprehensive income (loss)	(1.3)	(1.4)
Net income (loss)	(52.2)	(15.2)
Change in stockholder’s equity	(53.5)	(16.6)
Balance, end of period	250.3	364.8
COMMON STOCK:
Balance, beginning of period			2.5	2.5
Balance, end of period	2.5	2.5	2.5	2.5
ADDITIONAL PAID-IN CAPITAL:
Balance, beginning of period			862.2	847.2
Balance, end of period	862.2	847.2	862.2	847.2
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS):
Balance, beginning of period	4.0	(12.7)
Other comprehensive income (loss)	(1.3)	(1.4)
Balance, end of period	2.7	(14.1)
RETAINED EARNINGS (ACCUMULATED DEFICIT):
Balance, beginning of period	(564.9)	(455.6)
Net income (loss)	(52.2)	(15.2)
Balance, end of period	(617.1)	(470.8)
As reported
Balance, beginning of period		372.5
Other comprehensive income (loss)		(2.9)
Net income (loss)		(16.8)
Change in stockholder’s equity		(19.7)
Balance, end of period		352.8
As reported | COMMON STOCK:
Balance, beginning of period				2.5
Balance, end of period		2.5		2.5
As reported | ADDITIONAL PAID-IN CAPITAL:
Balance, beginning of period				847.2
Balance, end of period		847.2		847.2
As reported | ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS):
Balance, beginning of period		(11.9)
Other comprehensive income (loss)		(2.9)
Balance, end of period		(14.8)
As reported | RETAINED EARNINGS (ACCUMULATED DEFICIT):
Balance, beginning of period		(465.3)
Net income (loss)		(16.8)
Balance, end of period		(482.1)
Correction of errors
Balance, beginning of period		8.9
Net income (loss)		1.6
Change in stockholder’s equity		3.1
Balance, end of period		12.0
Correction of errors | COMMON STOCK:
Balance, beginning of period				0
Balance, end of period		0		0
Correction of errors | ADDITIONAL PAID-IN CAPITAL:
Balance, beginning of period				0
Balance, end of period		0		0
Correction of errors | ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS):
Balance, beginning of period		(0.8)
Other comprehensive income (loss)		1.5
Balance, end of period		0.7
Correction of errors | RETAINED EARNINGS (ACCUMULATED DEFICIT):
Balance, beginning of period		9.7
Net income (loss)		1.6
Balance, end of period		$ 11.3