Equity-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Share-based Compensation [Abstract]
Shares available for future grants	10,900,000
Options Outstanding [RollForward]
Excess tax benefit on share-based compensation	$ 0.6		$ (1.0)
Weighted-Average Price [Abstract]
Share-based compensation	6.8		6.1
Stock Options [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair value of options at grant date	$ 10.12
Risk-free interest rate (in hundredths)	1.31%
Expected price volatility (in hundredths)	37.20%
Expected dividend yield (in hundredths)	0.25%
Expected life in years	4 years 6 months
Options Outstanding [RollForward]
Outstanding Beginning Balance (in shares)	1,794,187
Granted (in shares)	279,458
Exercised (in shares)	(29,479)
Outstanding Ending Balance (in shares)	2,044,166
Options Excercisable (in shares)	1,480,337
Unvested Options (in shares)	563,829
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)	$ 23.01
Weighted-Average Price, Ending (in dollars per share)	$ 28.49
Weighted-Average Price, Options Excercisable	$ 27.56
Weighted-Average Price, Unvested Options	$ 30.93
Weighted-Average Remaining Contractual Term, Outstanding	3 years 10 months 27 days
Aggregate Intrinsic Value, Outstanding	5.2
Weighted-Average Remaining Contractual Term, Options Excercisable	3 years 0 months 7 days
Aggregate Intrinsic Value, Options Excercisable	5.1
Weighted-Average Remaining Contractual Term, Unvested Options	6 years 2 months 26 days
Aggregate Intrinsic Value, Unvested Options	0.1
Intrinsic value of options exercised	0.2		4.2
Unrecognized compensation cost	4.7
Weighted-average period for recognition of compensation costs	2 years 5 months 4 days
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options	0.7
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	0.1		1.4
Restricted Stock [Member]
Options Outstanding [RollForward]
Total fair value of stock that vested	15.1		14.8
Shares Outstanding [Roll Forward]
Balance, beginning (in shares)	1,388,953
Granted (in shares)	844,552
Vested and paid out (in shares)	(524,672)
Forfeited (in shares)	(18,170)
Balance, Ending (in shares)	1,690,663
Weighted-Average Price [Abstract]
Weighted-Average Price, Forfeited (in dollars per share)	$ 31.28
Weighted-Average Price, beginning balance (in dollars per share)	$ 30.96
Weighted-Average Price, Granted (in dollars per share)	$ 31.69		$ 30.12
Weighted-Average Price, Vested and paid out (in dollars per share)	$ 31.89
Weighted-Average Price, Ending Balance (in dollars per share)	$ 31.03
Unrecognized compensation cost	35.5
Weighted-average period for recognition of compensation costs	2 years 6 months 10 days
Vesting period (in years)	3 years 0 months 0 days
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	1.5		0.3
Performance Share Units [Member]
Shares Outstanding [Roll Forward]
Balance, beginning (in shares)	480,660
Granted (in shares)	241,321
Vested and paid out (in shares)	(55,659)
Vested and canceled (in shares)	(51,361)	[1]
Balance, Ending (in shares)	614,961
Weighted-Average Price [Abstract]
Weighted-Average Price, beginning balance (in dollars per share)	$ 32.33
Weighted-Average Price, Granted (in dollars per share)	$ 31.69		$ 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)	$ 30.90
Unrecognized compensation cost	12.8
Weighted-average period for recognition of compensation costs	2 years 4 months 24 days
QEP Midstream Long-Term Incentive Plan [Member]
Weighted-Average Price [Abstract]
Share-based compensation	$ 0.4

[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.