Debt Short-term Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Short-term Debt [Line Items]
Commercial paper with variable-interest rates	$ 219,000,000		$ 263,000,000
Revolving credit arrangement [Member]
Short-term Debt [Line Items]
Revolving credit arrangement credit commitments	350,000,000		500,000,000
Additional Long-Term Borrowing Permitted Under Credit Arrangement Amendment			150,000,000
Consolidated Funded Debt Percentage Of Consolidated Capital Permitted Under Credit Arrangement Amendment			70.00%
Debt Instrument Maturity Dates	2016-08	2013-07
Commercial paper [Member]
Short-term Debt [Line Items]
Commercial paper with variable-interest rates	219,000,000		263,000,000
Short-term Debt, Weighted Average Interest Rate	0.29%		0.31%
Questar Gas [Member]
Short-term Debt [Line Items]
Notes payable to parent	142,700,000		166,100,000
Questar Gas [Member] | Notes payable to Questar [Member]
Short-term Debt [Line Items]
Notes payable to parent	142,700,000		166,100,000
Short-term Debt, Weighted Average Interest Rate	0.41%		0.39%
Questar Pipeline [Member] | Notes payable to Questar [Member]
Short-term Debt [Line Items]
Notes payable to parent	$ 0		$ 0