Impairment of Long-Lived Assets	9 Months Ended
Sep. 30, 2015
Impairment of Long-Lived Assets [Abstract]
Impairment of Long-Lived Assets	IMPAIRMENT OF LONG-LIVED ASSETS Impairment of Lignite/Coal Fueled Generation and Mining Assets We evaluated our generation assets for impairment during September 2015 as a result of an impairment indicator related to the continued decline in forecasted wholesale electricity prices in ERCOT. Our evaluation concluded that impairments existed at our Martin Lake, Sandow 4 and Sandow 5 generation facilities, and the carrying value for those facilities and related mining facilities were reduced in total by $1.295 billion. Our fair value measurement for these assets was determined based on an income approach that utilized probability-weighted estimates of discounted future cash flows, which were Level 3 fair value measurements (see Note 12). Key inputs into the fair value measurement for these assets included current forecasted wholesale electricity prices in ERCOT, forecasted fuel prices, capital and operating expenditure forecasts and discount rates. We evaluated our generation assets for impairment during March 2015 as a result of an impairment indicator related to lower forecasted wholesale electricity prices in ERCOT. Our evaluation concluded that an impairment existed at our Big Brown generation facility, and the carrying value for that facility and related mining facility was reduced by $676 million. Our fair value measurement for these assets was determined based on an income approach that utilized probability-weighted estimates of discounted future cash flows, which were Level 3 fair value measurements (see Note 12). Key inputs into the fair value measurement for these assets included current forecasted wholesale electricity prices in ERCOT, forecasted fuel prices, capital and operating expenditure forecasts and discount rates. In July 2015, we filed notice with ERCOT that we intend to seasonally suspend operations at a second of the three units at our Martin Lake generation facility, with the units returning to service for the peak demand months of summer. In June 2015, we also assessed whether this planned notice constituted an impairment indicator for the Martin Lake generation facility and concluded that since the decision is expected to result in improved cash flows for the plant, it was not an indicator of impairment. In the three and nine months ended September 30, 2014, we wrote off previously incurred and deferred costs totaling $9 million and $30 million, respectively, for mining projects not expected to be completed due to economic forecasts and regulatory uncertainty. These charges have been recorded in impairment of long-lived assets. Additional material impairments may occur in the future with respect to these assets or other of our generation facilities if forward wholesale electricity prices continue to decline or forecasted costs of producing electricity at our generation facilities increase.

IMPAIRMENT OF LONG-LIVED ASSETS

Impairment of Lignite/Coal Fueled Generation and Mining Assets

We evaluated our generation assets for impairment during September 2015 as a result of an impairment indicator related to the continued decline in forecasted wholesale electricity prices in ERCOT. Our evaluation concluded that impairments existed at our Martin Lake, Sandow 4 and Sandow 5 generation facilities, and the carrying value for those facilities and related mining facilities were reduced in total by $1.295 billion. Our fair value measurement for these assets was determined based on an income approach that utilized probability-weighted estimates of discounted future cash flows, which were Level 3 fair value measurements (see Note 12). Key inputs into the fair value measurement for these assets included current forecasted wholesale electricity prices in ERCOT, forecasted fuel prices, capital and operating expenditure forecasts and discount rates.

We evaluated our generation assets for impairment during March 2015 as a result of an impairment indicator related to lower forecasted wholesale electricity prices in ERCOT. Our evaluation concluded that an impairment existed at our Big Brown generation facility, and the carrying value for that facility and related mining facility was reduced by $676 million. Our fair value measurement for these assets was determined based on an income approach that utilized probability-weighted estimates of discounted future cash flows, which were Level 3 fair value measurements (see Note 12). Key inputs into the fair value measurement for these assets included current forecasted wholesale electricity prices in ERCOT, forecasted fuel prices, capital and operating expenditure forecasts and discount rates.

In July 2015, we filed notice with ERCOT that we intend to seasonally suspend operations at a second of the three units at our Martin Lake generation facility, with the units returning to service for the peak demand months of summer. In June 2015, we also assessed whether this planned notice constituted an impairment indicator for the Martin Lake generation facility and concluded that since the decision is expected to result in improved cash flows for the plant, it was not an indicator of impairment.

In the three and nine months ended September 30, 2014, we wrote off previously incurred and deferred costs totaling $9 million and $30 million, respectively, for mining projects not expected to be completed due to economic forecasts and regulatory uncertainty. These charges have been recorded in impairment of long-lived assets.

Additional material impairments may occur in the future with respect to these assets or other of our generation facilities if forward wholesale electricity prices continue to decline or forecasted costs of producing electricity at our generation facilities increase.