Derivative Contracts Gain (Loss) in Statement of Financial Performance (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss) derivative contracts not designated as hedging instruments	$ (11.1)	$ 147.6	$ 370.3
Unrealized gain (loss) derivative contracts not designated as hedging instruments	374.4	(88.7)	63.2
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	363.3	58.9	433.5
Realized and unrealized gains on commodity derivative instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	(3.5)	150.3	371.6
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	372.4	(92.8)	69.3
Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments	368.9	57.5	440.9
Natural gas derivative contracts [Member] | Realized and unrealized gains on commodity derivative instruments [Member] | QEP Energy [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	(16.7)	152.0	341.9
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	68.4	(42.6)	37.8
Natural gas derivative contracts [Member] | Realized and unrealized gains on commodity derivative instruments [Member] | QEP Marketing [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	(2.5)	0.5	5.1
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	4.2	(2.1)	0.9
NGL derivative contracts [Member] | Realized and unrealized gains on commodity derivative instruments [Member] | QEP Energy [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	0	0	10.2
Unrealized gain (loss) derivative contracts not designated as hedging instruments	0	0	1.6
Oil derivative contracts [Member] | Realized and unrealized gains on commodity derivative instruments [Member] | QEP Energy [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	15.7	(2.2)	14.4
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	299.8	(48.1)	29.0
Interest Rate Swap [Member] | Realized And Unrealized Gains Losses On Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss) on commodity derivative contracts not designated as hedging instruments	(7.6)	(2.7)	(1.3)
Unrealized gain (loss) on commodity derivative contracts not designated as hedging instruments	2.0	4.1	(6.1)
Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments	$ (5.6)	$ 1.4	$ (7.4)