Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Commitments for demand charges under existing long-term contracts and binding precedent agreements with various pipelines
Remedial action included in other credits	$ 0.6
Pipeline demand charges
Commitments for demand charges under existing long-term contracts and binding precedent agreements with various pipelines
Amount due as of the balance sheet date	2,167.8
Amount due in 2014	140.8
Amount due in 2015	192.4
Amount due in 2016	184.8
Amount due in 2017	180.8
Amount due in 2018	180.8
Thereafter	1,288.2
Drilling equipment and services supply agreements
Commitments for demand charges under existing long-term contracts and binding precedent agreements with various pipelines
Amount due as of the balance sheet date	$ 70.4