CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)		$ (1,245.0)	$ (149.4)	$ 784.4
Pension and other postretirement plans adjustments:
Current year prior service cost	[1]	0.0	(0.6)	0.0
Current year net actuarial gain (loss)	[2]	(5.6)	(0.5)	(13.6)
Amortization of net prior service cost	[3]	0.8	8.2	9.7
Amortization of net actuarial loss	[4]	0.5	0.3	0.5
Net curtailment and settlements cost incurred	[5]	0.0	4.5	5.6
Other comprehensive income		(4.3)	11.9	2.2
Comprehensive income (loss)		$ (1,249.3)	$ (137.5)	$ 786.6

[1] Presented net of income tax benefit of $0.3 million for the year ended December 31, 2015.

[2] Presented net of income tax benefit of $3.3 million, $0.3 million and $8.5 million for the years ended December 31, 2016, 2015 and 2014, respectively

[3] Presented net of income tax expense of $0.5 million, $4.9 million, and $6.0 million during the years ended December 31, 2016, 2015, and 2014, respectively.

[4] Presented net of income tax expense of $0.3 million, $0.2 million, and $0.3 million during the years ended December 31, 2016, 2015, and 2014, respectively.

[5] Presented net of income tax expense of $2.6 million and $3.5 million for the years ended December 31, 2015 and 2014, respectively.