Derivative Contracts Gain (Loss) in Statement of Financial Performance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative [Line Items]
Realized gain (loss) derivative contracts not designated as hedging instruments	$ 119.8	$ (8.4)	$ 316.5	$ (79.1)
Unrealized gain (loss) derivative contracts not designated as hedging instruments	33.8	164.1	(148.0)	65.9
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	153.6	155.7	168.5	(13.2)
Realized and unrealized gains on commodity derivative instruments [Member]
Derivative [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	119.8	(7.1)	316.5	(75.9)
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	33.8	161.5	(148.0)	64.8
Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments	153.6	154.4	168.5	(11.1)
Natural gas derivative contracts [Member] | Realized and unrealized gains on commodity derivative instruments [Member] | QEP Energy [Member]
Derivative [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	23.1	5.5	69.1	(23.3)
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	3.6	27.6	(19.5)	9.5
Natural gas derivative contracts [Member] | Realized and unrealized gains on commodity derivative instruments [Member] | QEP Marketing [Member]
Derivative [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	(0.1)	(0.4)	2.1	(2.4)
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	1.4	0.7	(0.5)	1.0
Oil derivative contracts [Member] | Realized and unrealized gains on commodity derivative instruments [Member] | QEP Energy [Member]
Derivative [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	96.8	(12.2)	245.3	(50.2)
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	28.8	133.2	(128.0)	54.3
Interest Rate Swap [Member] | Realized And Unrealized Gains Losses On Interest Rate Swaps [Member]
Derivative [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	0.0	(1.3)	0.0	(3.2)
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments	0.0	2.6	0.0	1.1
Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments	$ 0.0	$ 1.3	$ 0.0	$ (2.1)