Derivatives and Hedge Accounting Activities - Schedule of Fair Values of Derivatives and Balance Sheet Location (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivatives assets			$ 0.1
Derivative liabilities		$ 1.3	0.1
Current Assets
Derivatives, Fair Value [Line Items]
Derivatives assets	[1]		0.1
Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	[2]	0.1	0.1
Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	[3]	1.2
Fair Value - Derivatives not under Hedge Accounting
Derivatives, Fair Value [Line Items]
Derivatives assets			0.1
Derivative liabilities		1.3	0.1
Fair Value - Derivatives not under Hedge Accounting | Current Assets
Derivatives, Fair Value [Line Items]
Derivatives assets	[1]		0.1
Fair Value - Derivatives not under Hedge Accounting | Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	[2]	0.1	0.1
Fair Value - Derivatives not under Hedge Accounting | Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	[3]	1.2
Commodity | Current Assets
Derivatives, Fair Value [Line Items]
Derivatives assets			0.1
Commodity | Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities		0.1	0.1
Commodity | Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities		1.2
Commodity | Fair Value - Derivatives not under Hedge Accounting | Current Assets
Derivatives, Fair Value [Line Items]
Derivatives assets			0.1
Commodity | Fair Value - Derivatives not under Hedge Accounting | Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities		0.1	$ 0.1
Commodity | Fair Value - Derivatives not under Hedge Accounting | Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities		$ 1.2

[1] Current derivative assets are presented in other current assets in Questar Gas' Balance Sheets.

[2] Current derivative liabilities are presented in other current liabilities in Questar Gas’ Balance Sheets.

[3] Noncurrent derivative liabilities are presented in other noncurrent liabilities in Questar Gas' Balance Sheets.