Basis of Presentation of Interim Consolidated Financial Statements Impairment of Long-Lived Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Asset Impairment Charges			$ 20.5	$ 3.5
Continuing Operations [Member]
Asset Impairment Charges	$ 0.5	$ 1.5	20.5	$ 3.5
Proved Property [Member]
Asset Impairment Charges			19.4
Southern Region [Member]
Asset Impairment Charges			14.5
Unproved Property [Member]
Asset Impairment Charges			1.1
Northern Region [Member]
Asset Impairment Charges			$ 4.9