Regulatory Matters	12 Months Ended
Dec. 31, 2013
Regulated Operations [Abstract]
Regulatory Matters	Regulatory Matters Hydro Transaction In December 2013, we submitted a filing with the MPSC requesting approval of the Hydro Transaction. The filing initiates the formal regulatory process necessary to complete the previously announced $900 million agreement, and includes a request to include the hydro assets in rate base and to issue the securities necessary to complete the purchase. The request is based on a return on equity of 10.0%, a capital structure of 52% debt and 48% equity, and an estimated rate base of $866 million. The MPSC has established a procedural schedule and we expect the MPSC to issue a decision during the second half of 2014. In January 2014, we made three separate applications with the FERC necessary for the Hydro Transaction, respectively seeking (1) approval of the asset transfer itself, (2) authorization to continue making wholesale power sales at market-based rates after the transaction and (3) approval to transfer the four associated FERC hydroelectric licenses. We anticipate that FERC will act before the June 30, 2014, requested action date for the first two applications. On January 17, 2014, the CSKT protested the third application to transfer the FERC hydro licenses on procedural grounds and asked FERC to reject the application with respect to the Kerr Project. PPL Montana responded to the CSKT’s motion on January 27, 2014, but FERC has yet to rule. We requested FERC action on this third application by April 30, 2014. Dave Gates Generating Station at Mill Creek (DGGS) As a result of a FERC ALJ nonbinding decision issued in September 2012, we have cumulative deferred revenue of approximately $24.5 million, which is subject to refund and recorded within current regulatory liabilities in the Consolidated Balance Sheets. The ALJ concluded we should allocate only a fraction of the costs we believe (based on past practice) should be allocated to FERC jurisdictional customers. The matter has been fully briefed before the FERC. We do not know when the FERC will consider the matter and issue its decision. The FERC is not obligated to follow any of the ALJ's findings and conclusions, and the FERC can accept or reject the decision in whole or in part. If the FERC upholds the ALJ's decision and a portion of the costs are effectively disallowed, we would be required to assess DGGS for impairment. If we disagree with a decision issued by the FERC, we may pursue full appellate rights through rehearing and appeal to a United States Circuit Court of Appeals, which could extend into 2015 or beyond. We continue to bill FERC jurisdictional customers interim rates that have been in effect since January 1, 2011. These interim rates are subject to refund plus interest pending final resolution at FERC. Montana Electric and Natural Gas Tracker Filings Each year we submit electric and natural gas tracker filings for recovery of supply costs for the 12-month period ended June 30 and for the projected supply costs for the next 12-month period. The MPSC reviews such filings and makes its cost recovery determination based on whether or not our electric and natural gas supply procurement activities were prudent. In its April 2012 electric supply tracker order for the 2010/2011 tracker period, the MPSC had authorized us to include forecasted DSM lost revenues in future tracker filings. We had not recognized the entire forecasted amount for tracker periods since 2010/2011 as we were required to provide the MPSC with a detailed independent study supporting our requested DSM lost revenues. During October 2013, the MPSC approved an order related to our 2012 electric supply tracker filing (covering July 1, 2011 through June 30, 2012), which includes a decision on a review of an independent study related to our request for DSM lost revenues, addresses future DSM lost revenue recovery, and includes a decision on DGGS related incremental contract costs included in the 2012 filing. Based on the MPSC's October 2013 decision we recognized revenue of approximately $3.8 million related to prior periods (including $1.9 million related to calendar year 2012) that we had previously deferred pending outcome of the review of the study results. The order also includes a provision expressing concern with the policy of continuing to allow DSM lost revenue recovery, indicating that we bear the burden of demonstrating why any incremental DSM lost revenue recovery from the date of its order forward is reasonable and in the public interest. As of December 31, 2013, we have recognized approximately $7.1 million of DSM lost revenues for the 2012/ 2013 tracker period and approximately $3.6 million for the 2013/2014 tracker period. Based on the MPSC's order, we expect to be able to collect at least $7.1 million of DSM lost revenues for each annual tracker period; however, since the 2012/2013 annual tracker filing is still subject to final approval, the MPSC may ultimately require us to refund a portion of the DSM lost revenues we have recognized since July 2012. We do not expect the MPSC to issue a final order related to 2012/2013 DSM lost revenues until at least the first quarter of 2014. Last, the MPSC indicated that $1.4 million of incremental costs associated with regulation service acquired from third parties during a 2012 outage at DGGS were imprudently incurred, and disallowed recovery. While we recognized revenues and expenses consistent with the MPSC order, we appealed the MPSC's decision to the District Court in Montana in December 2013. Natural Gas Production Assets We purchased additional natural gas production interests in northern Montana's Bear Paw Basin during 2013 and 2012. We are collecting the cost of service for natural gas produced from these assets, including a return on our investment, through our natural gas supply tracker on an interim basis. As a result, we do not expect to file an application with the MPSC to place these assets in natural gas rate base until our next natural gas rate case. We are recognizing Bear Paw related revenue based on the precedent established by the MPSC's approval of Battle Creek in the fourth quarter of 2012. Since acquisition, we have recognized approximately $7.0 million of revenue that is subject to refund.

Regulatory Matters

Hydro Transaction

In December 2013, we submitted a filing with the MPSC requesting approval of the Hydro Transaction. The filing initiates the formal regulatory process necessary to complete the previously announced $900 million agreement, and includes a request to include the hydro assets in rate base and to issue the securities necessary to complete the purchase. The request is based on a return on equity of 10.0%, a capital structure of 52% debt and 48% equity, and an estimated rate base of $866 million. The MPSC has established a procedural schedule and we expect the MPSC to issue a decision during the second half of 2014.

In January 2014, we made three separate applications with the FERC necessary for the Hydro Transaction, respectively seeking (1) approval of the asset transfer itself, (2) authorization to continue making wholesale power sales at market-based rates after the transaction and (3) approval to transfer the four associated FERC hydroelectric licenses. We anticipate that FERC will act before the June 30, 2014, requested action date for the first two applications. On January 17, 2014, the CSKT protested the third application to transfer the FERC hydro licenses on procedural grounds and asked FERC to reject the application with respect to the Kerr Project. PPL Montana responded to the CSKT’s motion on January 27, 2014, but FERC has yet to rule. We requested FERC action on this third application by April 30, 2014.

Dave Gates Generating Station at Mill Creek (DGGS)

As a result of a FERC ALJ nonbinding decision issued in September 2012, we have cumulative deferred revenue of approximately $24.5 million, which is subject to refund and recorded within current regulatory liabilities in the Consolidated Balance Sheets. The ALJ concluded we should allocate only a fraction of the costs we believe (based on past practice) should be allocated to FERC jurisdictional customers. The matter has been fully briefed before the FERC.

We do not know when the FERC will consider the matter and issue its decision. The FERC is not obligated to follow any of the ALJ's findings and conclusions, and the FERC can accept or reject the decision in whole or in part. If the FERC upholds the ALJ's decision and a portion of the costs are effectively disallowed, we would be required to assess DGGS for impairment. If we disagree with a decision issued by the FERC, we may pursue full appellate rights through rehearing and appeal to a United States Circuit Court of Appeals, which could extend into 2015 or beyond. We continue to bill FERC jurisdictional customers interim rates that have been in effect since January 1, 2011. These interim rates are subject to refund plus interest pending final resolution at FERC.

Montana Electric and Natural Gas Tracker Filings

Each year we submit electric and natural gas tracker filings for recovery of supply costs for the 12-month period ended

June 30 and for the projected supply costs for the next 12-month period. The MPSC reviews such filings and makes its cost recovery determination based on whether or not our electric and natural gas supply procurement activities were prudent.

In its April 2012 electric supply tracker order for the 2010/2011 tracker period, the MPSC had authorized us to include forecasted DSM lost revenues in future tracker filings. We had not recognized the entire forecasted amount for tracker periods since 2010/2011 as we were required to provide the MPSC with a detailed independent study supporting our requested DSM lost revenues.

During October 2013, the MPSC approved an order related to our 2012 electric supply tracker filing (covering July 1, 2011 through June 30, 2012), which includes a decision on a review of an independent study related to our request for DSM lost revenues, addresses future DSM lost revenue recovery, and includes a decision on DGGS related incremental contract costs included in the 2012 filing. Based on the MPSC's October 2013 decision we recognized revenue of approximately $3.8 million related to prior periods (including $1.9 million related to calendar year 2012) that we had previously deferred pending outcome of the review of the study results.

The order also includes a provision expressing concern with the policy of continuing to allow DSM lost revenue recovery, indicating that we bear the burden of demonstrating why any incremental DSM lost revenue recovery from the date of its order forward is reasonable and in the public interest. As of December 31, 2013, we have recognized approximately $7.1 million of DSM lost revenues for the 2012/ 2013 tracker period and approximately $3.6 million for the 2013/2014 tracker period. Based on the MPSC's order, we expect to be able to collect at least $7.1 million of DSM lost revenues for each annual tracker period; however, since the 2012/2013 annual tracker filing is still subject to final approval, the MPSC may ultimately require us to refund a portion of the DSM lost revenues we have recognized since July 2012. We do not expect the MPSC to issue a final order related to 2012/2013 DSM lost revenues until at least the first quarter of 2014.

Last, the MPSC indicated that $1.4 million of incremental costs associated with regulation service acquired from third parties during a 2012 outage at DGGS were imprudently incurred, and disallowed recovery.

While we recognized revenues and expenses consistent with the MPSC order, we appealed the MPSC's decision to the District Court in Montana in December 2013.

Natural Gas Production Assets

We purchased additional natural gas production interests in northern Montana's Bear Paw Basin during 2013 and 2012. We are collecting the cost of service for natural gas produced from these assets, including a return on our investment, through our natural gas supply tracker on an interim basis. As a result, we do not expect to file an application with the MPSC to place these assets in natural gas rate base until our next natural gas rate case. We are recognizing Bear Paw related revenue based on the precedent established by the MPSC's approval of Battle Creek in the fourth quarter of 2012. Since acquisition, we have recognized approximately $7.0 million of revenue that is subject to refund.