Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar's financial statements in this Annual Report:



	Hierarchy Level of Fair Value Estimates	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
		December 31, 2015				December 31, 2014
		(in millions)
Financial assets
Cash and cash equivalents	1	$	25.0	$	25.0	$	32.0	$	32.0
Long-term investment	1	14.1		14.1		15.7		15.7
Financial liabilities
Short-term debt	1	457.6		457.6		347.0		347.0
Long-term debt, including current portion	2	1,218.3		1,263.7		1,245.2		1,356.1

Questar Gas [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fair Value, by Balance Sheet Grouping



	Hierarchy Level of Fair Value Estimates	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
		December 31, 2015				December 31, 2014
		(in millions)
Financial assets
Cash and cash equivalents	1	$	10.5	$	10.5	$	19.8	$	19.8
Financial liabilities
Notes payable to Questar	1	273.3		273.3		119.3		119.3
Long-term debt	2	534.5		568.4		534.5		607.2

Questar Pipeline [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fair Value, by Balance Sheet Grouping



	Hierarchy Level of Fair Value Estimates	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
		December 31, 2015				December 31, 2014
		(in millions)
Financial assets
Cash and cash equivalents	1	$	10.2	$	10.2	$	7.4	$	7.4
Notes receivable from Questar	1	6.0		6.0		40.1		40.1
Financial liabilities
Long-term debt, including current portion	2	433.6		445.2		458.8		495.5