Employee Benefits Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension curtailment loss				$ 11.2	$ 0.0
Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost		$ 0.1	$ 0.0	0.2	0.2
Amortization of prior service costs	[1]	0.0	0.1	0.1	0.3
Pension curtailment loss	[2]	0.0	0.0	0.0	0.4
Periodic expense		0.1	0.1	0.3	0.9
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		0.5	0.6	1.5	2.0
Interest cost		1.3	1.2	3.7	4.0
Expected return on plan assets		(1.5)	(1.4)	(4.3)	(3.8)
Amortization of prior service costs	[1]	0.4	1.1	1.3	3.6
Amortization of actuarial losses	[1]	0.1	0.2	0.4	0.6
Pension curtailment loss	[2]	0.0	0.0	11.2	2.0
Special Termination Benefits	[3]	0.0	0.0	0.0	0.3
Periodic expense		$ 0.8	$ 1.7	$ 13.8	$ 8.7

[1] Amortization of prior service costs and actuarial losses out of accumulated other comprehensive income are recognized in the Condensed Consolidated Statements of Operations in "General and administrative."

[2] A curtailment is recognized immediately when there is a significant reduction in, or an elimination of, defined benefit accruals for current employees' future services. For the nine months ended September 30, 2015, these expenses are included on the Condensed Consolidated Statements of Operations within "General and administrative" expense as the expenses incurred in that period related to the Pension Plan amendment (see above). For the nine months ended September 30, 2014, these expenses are included within "Net gain (loss) from asset sales" as the expenses incurred in that period related to the Midcontinent property sales (see Note 3 – Acquisitions and Divestitures).

[3] During the nine months ended September 30, 2014, the Company recognized special termination benefits on the Condensed Consolidated Statements of Operations within "Net gain (loss) from asset sales" as the expense related to the Midcontinent property sales (see Note 3 – Acquisitions and Divestitures).