Gain (Loss) in Statement of Financial Performance (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) derivative contracts not designated as hedging instruments	$ (8.4)	$ 26.3	$ (79.1)	$ 107.1
Unrealized gain (loss) derivative contracts not designated as hedging instruments	164.1	(54.1)	65.9	(55.5)
Total gain (loss) on commodity derivative instruments	155.7	(27.8)	(13.2)	51.6
Realized and unrealized gains on commodity derivative instruments [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	(7.1)	26.9	(75.9)	109.0
Unrealized gain (loss) on commodity derivative contracts	161.5	(52.7)	64.8	(59.0)
Total gain (loss) on commodity derivative instruments	154.4	(25.8)	(11.1)	50.0
Natural gas derivative contracts [Member] | QEP Energy [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	5.5	42.5	(23.3)	112.0
Unrealized gain (loss) on commodity derivative contracts	27.6	(6.6)	9.5	(9.6)
Natural gas derivative contracts [Member] | QEP Marketing [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	(0.4)	(0.3)	(2.4)	0.7
Unrealized gain (loss) on commodity derivative contracts	0.7	0.1	1.0	(0.3)
Oil derivative contracts [Member] | QEP Energy [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	(12.2)	(15.3)	(50.2)	(3.7)
Unrealized gain (loss) on commodity derivative contracts	133.2	(46.2)	54.3	(49.1)
Interest Rate Swap [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	(1.3)	(0.6)	(3.2)	(1.9)
Unrealized gain (loss) on commodity derivative contracts	2.6	(1.4)	1.1	3.5
Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments	$ 1.3	$ (2.0)	$ (2.1)	$ 1.6