Regulatory Assets and Liabilities - Regulatory Liabilities (Details) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory liabilities		$ 9.1	$ 6.5	[1]
Regulatory liabilities, noncurrent		190.8	189.1	[1]
Total regulatory liabilities		199.9	195.6
CET
Regulatory Liabilities [Line Items]
Regulatory liabilities	[2]	2.3	2.9
Curtailment penalty
Regulatory Liabilities [Line Items]
Regulatory liabilities	[3]	1.1
Cost of plant removal and ARO's
Regulatory Liabilities [Line Items]
Regulatory liabilities	[4]	5.0	3.5
Regulatory liabilities, noncurrent	[4]	190.8	189.1
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities		$ 0.7	$ 0.1

[1] Questar Gas' Balance Sheet at December 31, 2016 has been derived from the audited Balance Sheet at that date.

[2] Represents the difference between actual and allowed revenues. Any deficiency in amounts collected is recovered through periodic rate adjustments.

[3] Interruptible customers who fail to interrupt service when called upon by Questar Gas incur a curtailment penalty. Penalties recovered by Questar Gas are credited to ratepayers as a reduction to the infrastructure-replacement program.

[4] Cost of plant removal and AROs represent amounts recovered from customers for costs of future activities to remove assets that are expected to be incurred at the time of retirement.