Rate and Regulatory Matters	9 Months Ended
Sep. 30, 2012
Rate and Regulatory Matters [Abstract]
RATE AND REGULATORY MATTERS	2. RATE AND REGULATORY MATTERS Rate Case Settlement Filing On April 26, 2012, the Federal Energy Regulatory Commission (FERC) unconditionally approved Northwest's Stipulation and Settlement Agreement (Settlement) filed on March 15, 2012. The supporting or non-opposing customers named in the Settlement represent approximately 99.5 percent of our long-term firm transportation and storage capacity. The Settlement specified an annual cost of service of $466.5 million and established a new general system firm transportation rate of $0.44 per dekatherm, a 7.4 percent increase over the current rate. New rates will become effective January 1, 2013, and will remain in effect for a minimum of 3 years and a maximum of 5 years.

Rate and Regulatory Matters

9 Months Ended

Sep. 30, 2012

Rate and Regulatory Matters [Abstract]

2. RATE AND REGULATORY MATTERS

Rate Case Settlement Filing

On April 26, 2012, the Federal Energy Regulatory Commission (FERC) unconditionally approved Northwest's Stipulation and Settlement Agreement (Settlement) filed on March 15, 2012. The supporting or non-opposing customers named in the Settlement represent approximately 99.5 percent of our long-term firm transportation and storage capacity. The Settlement specified an annual cost of service of $466.5 million and established a new general system firm transportation rate of $0.44 per dekatherm, a 7.4 percent increase over the current rate. New rates will become effective January 1, 2013, and will remain in effect for a minimum of 3 years and a maximum of 5 years.