Equity-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	10,900,000		10,900,000
Weighted-Average Price [Abstract]
Equity-based compensation	$ 6.6	$ 7.1	$ 13.4		$ 13.2
Stock Options [Member]
Options Outstanding [RollForward]
Outstanding Beginning Balance (in shares)			1,794,187
Granted (in shares)			282,236
Exercised (in shares)			(53,866)
Forfeited (in shares)			(14,842)
Outstanding Ending Balance (in shares)	2,007,715		2,007,715
Options Excercisable (in shares)	1,455,950		1,455,950
Unvested Options (in shares)	551,765		551,765
Weighted-Average Price [Abstract]
Weighted-Average Price, beginning (in dollars per share)			$ 27.90
Weighted-Average Price, Granted (in dollars per share)			$ 31.67
Weighted-Average Price, Exercised (in dollars per share)			$ 22.57
Weighted-Average Price, Forfeited (in dollars per share)			$ 30.53
Weighted-Average Price, Ending (in dollars per share)	$ 28.55		$ 28.55
Weighted-Average Price, Options Excercisable	$ 27.65		$ 27.65
Weighted-Average Price, Unvested Options	$ 30.94		$ 30.94
Weighted-Average Remaining Contractual Term, Outstanding			2 years 3 months 8 days
Aggregate Intrinsic Value, Outstanding	11.9		11.9
Weighted-Average Remaining Contractual Term, Options Excercisable			2 years 9 months 14 days
Aggregate Intrinsic Value, Options Excercisable	10.0		10.0
Weighted-Average Remaining Contractual Term, Unvested Options			5 years 11 months 26 days
Aggregate Intrinsic Value, Unvested Options	1.9		1.9
Intrinsic value of options exercised			0.5		4.2
Unrecognized compensation cost	3.8		3.8
Weighted-average period for recognition of compensation costs			2 years 2 months 16 days
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options			1.2
Restricted Stock [Member]
Options Outstanding [RollForward]
Total fair value of stock that vested			15.2		15.0
Shares Outstanding [Roll Forward]
Balance, beginning (in shares)			1,388,953
Granted (in shares)			886,783
Vested and paid out (in shares)			(525,651)
Forfeited (in shares)			(84,572)
Balance, Ending (in shares)	1,665,513		1,665,513
Weighted-Average Price [Abstract]
Weighted-Average Price, Forfeited (in dollars per share)			$ 30.93
Weighted-Average Price, beginning balance (in dollars per share)			$ 30.96
Weighted-Average Price, Granted (in dollars per share)			$ 31.63		$ 30.10
Weighted-Average Price, Vested and paid out (in dollars per share)			$ 31.89
Weighted-Average Price, Ending Balance (in dollars per share)	$ 31.03		$ 31.03
Unrecognized compensation cost	29.7		29.7
Weighted-average period for recognition of compensation costs			2 years 3 months 29 days
Vesting period (in years)			3 years 0 months 0 days
Performance Share Units [Member]
Shares Outstanding [Roll Forward]
Balance, beginning (in shares)			480,660
Granted (in shares)			247,192
Vested and paid out (in shares)			(55,659)
Forfeited (in shares)			(17,643)
Vested and canceled (in shares)			(51,361)	[1]
Balance, Ending (in shares)	603,189		603,189
Weighted-Average Price [Abstract]
Weighted-Average Price, Forfeited (in dollars per share)			$ 30.35
Weighted-Average Price, beginning balance (in dollars per share)			$ 32.33
Weighted-Average Price, Granted (in dollars per share)			$ 31.67		$ 30.12
Weighted-Average Price, Vested and paid out (in dollars per share)			$ 39.07
Weighted-Average Price, Vested and canceled (in dollars per share)			$ 39.07
Weighted-Average Price, Ending Balance (in dollars per share)	$ 30.92		$ 30.92
Unrecognized compensation cost	11.1		11.1
Weighted-average period for recognition of compensation costs			2 years 2 months 12 days
QEP Midstream Long-Term Incentive Plan [Member]
Weighted-Average Price [Abstract]
Equity-based compensation	$ 0.2		$ 0.6

[1] (1) Represents units that vested but were not paid out. Payout of the performance share units are dependent upon the Company’s total shareholder return compared to a group of its peers over a three-year period.