CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
OPERATING ACTIVITIES    
Net income $ 84.6 $ 85.1
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation, depletion and amortization 56.2 57.2
Deferred income taxes (3.8) (1.2)
Share-based compensation 3.2 3.2
(Income) from unconsolidated affiliate (0.9) (0.9)
Distributions from unconsolidated affiliate and other 1.5 1.6
Changes in operating assets and liabilities 82.6 67.9
Net Cash Provided By Operating Activities 223.4 212.9
INVESTING ACTIVITIES    
Property, plant and equipment (66.1) (69.7)
Questar Gas acquisition of gas distribution system (11.4) 0
Cash used in disposition of assets (0.6) (0.9)
Proceeds from disposition of assets 0.2 0
Net Cash Used In Investing Activities (77.9) (70.6)
FINANCING ACTIVITIES    
Common stock issued 1.3 0.5
Common stock repurchased (3.6) (2.8)
Change in short-term debt (133.0) (119.0)
Capital lease obligation repaid 0.3 0.3
Dividends paid (37.1) (31.6)
Tax benefits from share-based compensation 0 0.5
Net Cash Provided By (Used In) Financing Activities (172.7) (152.7)
Change in cash and cash equivalents (27.2) (10.4)
Beginning cash and cash equivalents 32.0 16.0
Ending cash and cash equivalents 4.8 5.6
Questar Gas [Member]    
OPERATING ACTIVITIES    
Net income 43.8 39.6
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 14.9 14.6
Deferred income taxes (2.4) (0.1)
Share-based compensation 0.3 0.3
Changes in operating assets and liabilities 80.0 45.3
Net Cash Provided By Operating Activities 136.6 99.7
INVESTING ACTIVITIES    
Property, plant and equipment (43.0) (48.9)
Questar Gas acquisition of gas distribution system (11.4) 0
Cash used in disposition of assets (0.5) (0.9)
Proceeds from disposition of assets 0.1 0
Net Cash Used In Investing Activities (54.8) (49.8)
FINANCING ACTIVITIES    
Change in notes receivable from Questar 0 (30.6)
Change in notes payable to Questar (83.5) (17.7)
Checks outstanding in excess of cash balances 0.4 0
Dividends paid to Questar (18.5) (9.0)
Net Cash Provided By (Used In) Financing Activities (101.6) (57.3)
Change in cash and cash equivalents (19.8) (7.4)
Beginning cash and cash equivalents 19.8 8.8
Ending cash and cash equivalents 0 1.4
Questar Pipeline [Member]    
OPERATING ACTIVITIES    
Net income 13.9 15.7
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 14.5 14.1
Deferred income taxes (0.2) (0.1)
Share-based compensation 0.5 0.6
(Income) from unconsolidated affiliate (0.9) (0.9)
Distributions from unconsolidated affiliate and other 1.3 1.5
Changes in operating assets and liabilities 6.2 13.0
Net Cash Provided By Operating Activities 35.3 43.9
INVESTING ACTIVITIES    
Property, plant and equipment (8.7) (8.5)
Cash used in disposition of assets (0.1) 0
Net Cash Used In Investing Activities (8.8) (8.5)
FINANCING ACTIVITIES    
Change in notes receivable from Questar 4.2 (17.2)
Dividends paid to Questar (32.0) (16.0)
Net Cash Provided By (Used In) Financing Activities (27.8) (33.2)
Change in cash and cash equivalents (1.3) 2.2
Beginning cash and cash equivalents 7.4 2.7
Ending cash and cash equivalents $ 6.1 $ 4.9