Supplemental Gas and Oil Information (Unaudited) Results of Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Results of Operations [Abstract]
Revenues (1)	$ 1,393.4	[1]	$ 1,703.4	[1]	$ 1,456.3	[1]
Production costs	501.1		433.3		330.6
Exploration expenses	11.2		10.5		23.0
Depreciation, depletion and amortization	838.0		707.2		592.5
Abandonment and impairment	133.4		218.4		46.1
Total expenses	1,483.7		1,369.4		992.2
Income before income taxes	(90.3)		334.0		464.1
Income taxes	33.6		(119.0)		(171.8)
Results of operations from producing activities excluding allocated corporate overhead and interest expenses	$ (56.7)		$ 215.0		$ 292.3

[1] Revenue for the years ended December 31, 2011 and 2010, reflect the impact of QEP's settled derivative contracts which during the year ended December 31, 2012, are reflected below operating (loss) income. See Note 6 - Derivative Contracts.