CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
COMMON SHAREHOLDERS' EQUITY
Common Stock, No Par Value	$ 0.00
Common Stock, Shares Authorized	500.0
Common Stock, Shares Outstanding	177.9	176.5
Questar Pipeline [Member]
COMMON SHAREHOLDERS' EQUITY
Common Stock, Par or Stated Value Per Share	$ 1.00
Common Stock, Shares Authorized	25.0
Common Stock, Shares, Issued	6.6	6.6
Common Stock, Shares Outstanding	6.6	6.6
Questar Gas [Member]
COMMON SHAREHOLDERS' EQUITY
Common Stock, Par or Stated Value Per Share	$ 2.50
Common Stock, Shares Authorized	50.0
Common Stock, Shares, Issued	9.2	9.2
Common Stock, Shares Outstanding	9.2	9.2