RELATED-PARTY TRANSACTIONS (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Services provided by related parties		$ 65.0	$ 55.7	$ 51.5
Services provided to related parties		3.2	6.7	6.1
Revolving Credit Facility | IRCA
Related Party Transaction [Line Items]
Interest charges		1.3
Transportation and storage services from affiliates
Related Party Transaction [Line Items]
Transportation and storage services from affiliates	[1]	72.9	73.0	$ 72.9
Dominion Questar Corporation | Revolving Credit Facility | IRCA
Related Party Transaction [Line Items]
Borrowings under the IRCA			$ 273.3
Dominion | Revolving Credit Facility | IRCA
Related Party Transaction [Line Items]
Borrowings under the IRCA		$ 48.0
Weighted-average interest rate percentage		1.04%
Dominion Questar Corporation | Dominion Questar Corporation | Merger and Restructuring Costs from Dominion Questar Combination
Related Party Transaction [Line Items]
Merger and restructuring costs		$ 13.8

[1] The costs of these services were included in cost of sales in Questar Gas' Statements of Income.