Derivative Contracts - Gain (Loss) in Statement of Financial Performance (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net [Abstract]
Fair value of frozen derivative to be settled and reclassified within twelve months			$ 97.7
Natural gas derivative contracts [Member] \| QEP Energy [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	86.2	(27.9)	283.8	(86.7)
Unrealized gain (loss) on commodity derivative contracts	(50.6)	27.9	3.3	86.7
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	3.7	0
Unrealized gain (loss) on commodity derivative contracts	(1.4)	0	(0.5)	0
Oil derivative contracts [Member] \| QEP Energy [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	2.7	0	2.2	0
Unrealized gain (loss) on commodity derivative contracts	4.1	0	31.2	0
NGL derivative contracts [Member] \| QEP Energy [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	3.4	0	6.5	0
Unrealized gain (loss) on commodity derivative contracts	(4.4)	0	3.4	0
NGL derivative contracts [Member] \| QEP Field Services [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	1.9	0	6.3	0
Unrealized gain (loss) on commodity derivative contracts	(2.5)	0	2.0	0
Interest Rate Swap [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	(0.6)	0	(0.6)	0
Unrealized gain (loss) on commodity derivative contracts	(2.3)	0	(6.6)	0
Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments	(2.9)	0	(7.2)	0
Total gain (loss) on commodity derivative instruments	36.1	0	334.7	0
Other Comprehensive Income (Loss) [Member]
Gain (loss) on derivative instruments for the effective portion of hedge recognized in AOCI [Abstract]
Gain on derivative instruments for the effective portion of hedge recognized in AOCI	0	129.6	0	191.1
Natural Gas Sales (MMbtu) [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Gain reclassified from AOCI into income for effective portion of hedge	0	71.6	0	209.1
NGL Sales [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Gain reclassified from AOCI into income for effective portion of hedge	0	(0.3)	0	(0.3)
Oil Sales (Bbls) [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Gain reclassified from AOCI into income for effective portion of hedge	0	0.9	0	1.0
QEP Marketing [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Gain reclassified from AOCI into income for effective portion of hedge	0	0	0	0
Marketing Purchases [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Gain reclassified from AOCI into income for effective portion of hedge	0	0.4	0	4.3
Interest Income [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net [Abstract]
Gain recognized in income for the ineffective portion of hedges	0	(2.7)	0	(2.6)
Realized and unrealized gains on commodity derivative instruments [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	93.8	(27.9)	302.5	(86.7)
Unrealized gain (loss) on commodity derivative contracts	(54.8)	27.9	39.4	86.7
Total gain (loss) on commodity derivative instruments	$ 39.0	$ 0	$ 341.9	$ 0

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Total Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments

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Represents the realized gain (loss) on commodity derivative contracts not designated as hedging instruments for the period.

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

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- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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- Definition

The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

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Net gain (loss) from the increase (decrease) in fair value of derivative instrument not designated as hedging instrument.

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Before tax amount of the change in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Also includes an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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