Earnings Per Share (Details) In Millions	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Common Share Attributable To Questar [Abstract]
Weighted-average basic common shares outstanding (in shares)	177.5	175.1	177.2	175.0	177.0	174.6
Potential number of shares issuable under the Long- Term Stock Incentive Plan (in shares)	1.3	2.5	1.5	2.4	2.0	2.3
Weighted average diluted common shares outstanding (in shares)	178.8	177.6	178.7	177.4	179.0	176.9

- Definition

Aggregate awards of share options and nonvested shares to be issued to an employee under a share-based compensation arrangement are considered options for purposes of computing diluted earnings per share. Such share-based awards shall be considered to be outstanding as of the grant date for purposes of computing diluted earnings per share even though their exercise may be contingent upon vesting. Those share-based awards are included in the diluted Earnings Per Share (EPS) computation even if the employee may not receive (or be able to sell) the stock until some future date. Accordingly, all shares to be issued shall be included in computing diluted EPS if the effect is dilutive. The dilutive effect of share-based compensation arrangements shall be computed using the treasury stock method. If the equity share options or other equity instruments are outstanding for only part of a period, the shares issuable shall be weighted to reflect the portion of the period during which the equity instruments were outstanding.

+ References+ Details