Fair Value Measurements (Schedule of Fair Value of the Level 3 Assets and Liabilities by Major Contract Type (All Related to Commodity Contracts) and the Significant Unobservable Inputs Used in the Valuations) (Details) - Level 3 [Member]
$ in Millions

9 Months Ended

12 Months Ended

Sep. 30, 2016

USD ($)

$ / Megawatt-hour

Dec. 31, 2015

USD ($)

$ / Megawatt-hour

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Assets

^[1]

$ 109

$ 49

Liabilities

^[1]

(12)

Derivative Assets (Liabilities), at Fair Value, Net

^[1]

Electricity purchases and sales [Member] | Valuation Model [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Assets

^[1]

Liabilities

^[1]

(1)

Derivative Assets (Liabilities), at Fair Value, Net

^[1]

Electricity spread options [Member] | Option Pricing Model Valuation Technique [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Assets

^[1]

Liabilities

^[1]

(4)

(7)

Derivative Assets (Liabilities), at Fair Value, Net

^[1]

(5)

Electricity congestion revenue rights [Member] | Market Approach [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Assets

^[1],[2]

Liabilities

^[1],[2]

(6)

(4)

Derivative Assets (Liabilities), at Fair Value, Net

^[1],[2]

Other [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Assets

^[1],[3]

Liabilities

^[1],[3]

(1)

Derivative Assets (Liabilities), at Fair Value, Net

^[1],[3]

$ 6

$ 7

Minimum [Member] | Electricity purchases and sales [Member] | Valuation Model [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Illiquid pricing locations (in usd per MWh) | $ / Megawatt-hour

^[1],[4],[5]

Hourly price curve shape (in usd per MWh) | $ / Megawatt-hour

^[1],[5],[6]

Fair Value Inputs Illiquid Delivery Periods For ERCOT Hub Power Prices And Heat Rates | $ / Megawatt-hour

^[1],[5],[7]

Minimum [Member] | Electricity spread options [Member] | Option Pricing Model Valuation Technique [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Gas to power correlation

^[1],[5],[8]

50.00%

35.00%

Power volatility

^[1],[5],[9]

10.00%

Minimum [Member] | Electricity congestion revenue rights [Member] | Market Approach [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Illiquid price differences between settlement points | $ / Megawatt-hour

^{[1],[2],[5],[10]}

Maximum [Member] | Electricity purchases and sales [Member] | Valuation Model [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Illiquid pricing locations (in usd per MWh) | $ / Megawatt-hour

^[1],[4],[5]

Hourly price curve shape (in usd per MWh) | $ / Megawatt-hour

^[1],[5],[6]

Fair Value Inputs Illiquid Delivery Periods For ERCOT Hub Power Prices And Heat Rates | $ / Megawatt-hour

^[1],[5],[7]

Maximum [Member] | Electricity spread options [Member] | Option Pricing Model Valuation Technique [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Gas to power correlation

^[1],[5],[8]

95.00%

80.00%

Power volatility

^[1],[5],[9]

60.00%

35.00%

Maximum [Member] | Electricity congestion revenue rights [Member] | Market Approach [Member]

Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]

Illiquid price differences between settlement points | $ / Megawatt-hour

^{[1],[2],[5],[10]}

[1]	Electricity purchase and sales contracts include power and heat rate hedging positions in the ERCOT regions. Electricity spread options contracts consist of physical electricity call options. Electricity congestion revenue rights contracts consist of forward purchase contracts (swaps and options) used to hedge electricity price differences between settlement points within ERCOT.
[2]	While we use the market approach, there is insufficient market data to consider the valuation liquid.
[3]	Other includes contracts for ancillary services, natural gas, power options, coal and coal options.
[4]	Based on the historical range of forward average monthly ERCOT hub and load zone prices.
[5]	The range of the inputs may be influenced by factors such as time of day, delivery period, season and location.
[6]	Based on the historical range of forward average hourly ERCOT North Hub prices.
[7]	Based on historical forward ERCOT power price and heat rate variability.
[8]	Estimate of the historical range based on forward natural gas and on-peak power prices for the ERCOT hubs most relevant to our spread options.
[9]	Based on historical forward price changes.
[10]	Based on the historical price differences between settlement points within the ERCOT hubs and load zones.

Energy Future Holdings Corp /TX/ 10-Q