Derivative Instruments and Hedging Activities (Tables)

3 Months Ended

Mar. 31, 2012

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative instruments on Consolidated Statements of Income and Accumulated Other Comprehensive Income

The following table presents the pre-tax effects of the derivative instruments designated as a fair value hedge (including the hedged item) and cash flow hedges on the Consolidated Statements of Income as well as the pre-tax effects of the derivative instruments designated as cash flow hedges on OCI:

		3 Months Ended					12 Months Ended
	Financial Statement	March 31,					March 31,
Instrument and Activity	Location of Gain (Loss)	2012			2011		2012			2011
		(in millions)
Fair Value Hedge
Questar Corporation
Interest rate derivative instrument
Realized gain	Interest expense	$	—		$	—	$	9.8		$	—
2.75% Notes due 2016
Unrealized loss	Interest expense	—			—		(9.8		)	—
Cash Flow Hedges
Questar Pipeline
Interest rate derivative instruments
Deferrals of effective portions	OCI	—			—		(37.3		)	—
Losses reclassified from AOCI into earnings for effective portions	Interest expense	(0.1		)	—		(0.2		)	—

Derivative instruments in Condensed Consolidated Balance Sheets

The following table discloses the Level 2 fair value of the derivative instrument designated as a fair value hedge in the Condensed Consolidated Balance Sheets:

Instrument	Balance Sheet Location	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011
		(in millions)
Assets
Questar Corporation
Interest rate derivative instrument	Prepaid expenses and other	$	—	$	—	$	1.1
Interest rate derivative instrument	Other noncurrent assets	—		—		7.8
Consolidated total - derivative assets		$	—	$	—	$	8.9