Derivative Contracts - Gain (Loss) in Statement of Financial Performance (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) derivative contracts not designated as hedging instruments	$ 378.7	$ (117.7)	$ (121.7)
Unrealized gain (loss) derivative contracts not designated as hedging instruments	63.2	117.7	121.7
Total gain (loss) on commodity derivative instruments	441.9	0	0
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	(171.1)
Natural gas derivative contracts [Member] \| QEP Energy [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	341.9	(117.7)	(121.7)
Unrealized gain (loss) on commodity derivative contracts	37.8	117.7	121.7
Natural gas derivative contracts [Member] \| QEP Marketing [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	5.1	0	0
Unrealized gain (loss) on commodity derivative contracts	0.9	0	0
Oil derivative contracts [Member] \| QEP Energy [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	14.4	0	0
Unrealized gain (loss) on commodity derivative contracts	29.0	0	0
NGL derivative contracts [Member] \| QEP Energy [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	10.2	0	0
Unrealized gain (loss) on commodity derivative contracts	1.6	0	0
NGL derivative contracts [Member] \| QEP Field Services [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	8.4	0	0
Unrealized gain (loss) on commodity derivative contracts	0	0	0
Interest Rate Swap [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	(1.3)	0	0
Unrealized gain (loss) on commodity derivative contracts	(6.1)	0	0
Realized and Unrealized Gain (Loss) on Commodity Derivative Contracts Not Designated as Hedging Instruments	(7.4)	0	0
Other Comprehensive Income (Loss) [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Gain on derivative instruments for the effective portion of hedge recognized in AOCI	0	350.8	565.8
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	305.5	353.8
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	(0.2)	0
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	1.6	(8.7)
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	4.3	3.1
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	0.1	0.2
Realized and unrealized gains on commodity derivative instruments [Member]
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Realized gain (loss) on commodity derivative contracts	380.0	(117.7)	(121.7)
Unrealized gain (loss) on commodity derivative contracts	69.3	117.7	121.7
Total gain (loss) on commodity derivative instruments	$ 449.3	$ 0	$ 0

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

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Realized gain (loss) derivative contracts not designated as hedging instruments

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- Definition

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

+ References

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Unrealized gain (loss) derivative contracts not designated as hedging instruments

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

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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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.

+ References

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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).

+ References

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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