CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)		$ 76.9	$ (863.8)
Postretirement medical plan change	[1]	1.6	0.0
Pension and other postretirement plans adjustments:
Amortization of prior service costs	[2]	0.1	0.1
Amortization of net actuarial losses	[3]	0.2	0.1
Other comprehensive income		1.9	0.2
Comprehensive income (loss)		78.8	(863.6)
Postretirement medical plan changes, income tax expense		(1.0)	0.0
Amortization of prior service cost, income tax expense		(0.1)	(0.1)
Amortization of net actuarial loss, income tax expense		$ (0.1)	$ (0.1)

[1] Presented net of income tax expense of $1.0 million during the three months ended March 31, 2017.

[2] Presented net of income tax expense of $0.1 million during the three months ended March 31, 2017 and 2016, respectively.

[3] Presented net of income tax expense of $0.1 million for the three months ended March 31, 2017 and 2016, respectively.