Employee Benefits (Tables)

12 Months Ended

Dec. 31, 2012

Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]

Schedule of Defined Benefit Plans Disclosures [Table Text Block]

The following table sets forth changes in the benefit obligations and fair value of plan assets for the Company's pension and other postretirement benefit plans for the years ended December 31, 2012 and 2011, as well as the funded status of the plans and amounts recognized in the financial statements at December 31, 2012 and 2011:

	Pension benefits						Other postretirement benefits
	2012			2011			2012			2011
	(in millions)
Change in benefit obligation
Benefit obligation at January 1,	$	104.1		$	78.0		$	5.9		$	4.5
Service cost	4.0			2.9			0.1			0.1
Interest cost	5.1			4.5			0.3			0.3
Change in plan assumptions	8.4			19.6			—			—
Benefit payments	(2.7		)	(0.2		)	—			—
Actuarial loss (gain)	10.8			(0.7		)	0.4			1.0
Benefit obligation at December 31,	$	129.7		$	104.1		$	6.7		$	5.9
Change in plan assets
Fair value of plan assets at January 1,	$	44.2		$	30.9		$	—		$	—
Actual gain (loss) on plan assets	6.9			(1.3		)	—			—
Company contributions to the plan	6.9			14.8			—			—
Benefit payments	(2.7		)	(0.2		)	—			—
Fair value of plan assets at December 31,	55.3			44.2			—			—
Underfunded status (current and long-term)	$	(74.4	)	$	(59.9	)	$	(6.7	)	$	(5.9	)
Amounts recognized in balance sheets
Accounts payable and accrued expenses	$	(3.2	)	$	(1.3	)	$	(0.2	)	$	—
Other long-term liabilities	(71.2		)	(58.6		)	(6.5		)	(5.9		)
Total amount recognized in balance sheet	$	(74.4	)	$	(59.9	)	$	(6.7	)	$	(5.9	)
Amounts recognized in AOCI
Net actuarial loss (gain)	$	32.6		$	18.6		$	1.3		$	1.0
Prior service cost	35.1			42.6			3.4			3.8
Total amount recognized in AOCI	$	67.7		$	61.2		$	4.7		$	4.8

Pension and Other Postretirement Benefit Costs

The following table sets forth the Company's pension and other postretirement benefit cost and amounts recognized in other comprehensive income (before tax) for the respective years ended December 31:

	Pension benefits									Other postretirement benefits
	2012			2011			2010			2012			2011			2010
Components of net periodic benefit cost
Service cost	$	4.0		$	2.9		$	1.3		$	0.1		$	0.1		$	0.1
Interest cost	5.1			4.5			2.1			0.3			0.3			0.1
Expected return on plan assets	(3.6		)	(2.6		)	(1.1		)	—			—			—
Curtailment loss	2.2			—			—			—			—			—
Amortization of prior service costs	5.3			5.3			2.6			0.3			0.3			0.2
Amortization of actuarial loss	1.9			—			—			0.1			—			—
Periodic expense	$	14.9		$	10.1		$	4.9		$	0.8		$	0.7		$	0.4
Components recognized in accumulated other comprehensive income
Current period actuarial loss (gain)	$	15.9		$	22.9		$	(4.2	)	$	0.4		$	1.0		$	—
Amortization of actuarial loss	(1.9		)	—			—			(0.1		)	—			—
Current period prior service cost	—			—			50.4			—			—			4.3
Amortization of prior service cost	(5.3		)	(5.3		)	(2.6		)	(0.4		)	(0.3		)	(0.1		)
Loss on curtailment in current period	(2.2		)	—			—			—			—			—
Total amount recognized in accumulated other comprehensive income	$	6.5		$	17.6		$	43.6		$	(0.1	)	$	0.7		$	4.2

Schedule of Assumptions Used [Table Text Block]

Following are the weighted-average assumptions (weighted by the plan level benefit obligation for pension benefits) used by the Company to calculate pension and other postretirement benefit obligations at December 31, 2012 and 2011:

	Pension benefits				Other postretirement benefits
	2012		2011		2012		2011
Discount rate	3.88	%	4.54	%	4.10	%	4.70	%
Rate of increase in compensation	3.60	%	3.60	%	3.60	%	4.00	%

The discount rate assumptions used by the Company represents an estimate of the interest rate at which the pension and other postretirement obligations could effectively be settled on the measurement date.

Following are the weighted-average assumptions (weighted by the net period benefit cost for pension benefits) used by the Company in determining the net periodic pension and other postretirement benefit cost for the years ended December 31:

	Pension benefits						Other postretirement benefits
	2012		2011		2010		2012		2011		2010
Discount rate	4.38	%	5.80	%	5.70	%	4.70	%	5.80	%	5.70	%
Expected long-term return on plan assets	7.25	%	7.50	%	7.50	%	n/a		n/a		n/a
Rate of increase in compensation	3.60	%	3.60	%	3.60	%	4.00	%	n/a		n/a

Defined Benefit Plan, Actual Plan Asset Allocations [Abstract] (Deprecated 2012-01-31)

The following table sets forth by level, within the fair value hierarchy, the fair value of pension and postretirement benefit assets.:

	As of December 31, 2012								Percentage of total
	Level 1		Level 2		Level 3		Total
	(in millions except percentages)
Cash and short-term investments	$	—	$	—	$	0.2	$	0.2	—		%
Equity securities:
Domestic	—		—		22.2		22.2		40		%
International	—		—		16.7		16.7		30		%
Fixed income	—		—		16.2		16.2		30		%
Total investments	—		—		$	55.3	$	55.3	100		%
	As of December 31, 2011								Percentage of total
	Level 1		Level 2		Level 3		Total
	(in millions except percentages)
Cash and short-term investments	$	—	$	—	$	—	$	—	$	—
Equity securities:
Domestic	—		—		17.6		17.6		40		%
International	—		—		13		13.0		29		%
Fixed income	—		—		13.6		13.6		31		%
Total investments	—		—		$	44.2	$	44.2	100		%

Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets [Table Text Block]

The following table presents a summary of changes in the fair value of QEP's Level 3 investments:

	Year ended December 31,
	2012			2011
	(in millions)
Balance at January 1,	$	44.2		30.9
Employer contributions	5.6			14.8
Unrealized gains (losses)	6.3			(1.4		)
Realized gains	0.7			0.3
Administrative fees	(0.2		)	(0.2		)
Benefits paid	(1.3		)	(0.2		)
Balance at December 31,	$	55.3		$	44.2

Schedule of Expected Benefit Payments [Table Text Block]

Expected Benefit Payments

As of December 31, 2012, the following future benefit payments are expected to be paid:

	Pension		Postretirement benefits
	(in millions)
2013	$	5.7	$	0.2
2014	5.3		0.2
2015	4.9		0.2
2016	5.6		0.3
2017	5.2		0.3
2018 through 2021	40.9		1.8