Business and Basis of Presentation (Detail) $ / shares in Units, $ in Millions		1 Months Ended	5 Months Ended		6 Months Ended
		Jun. 30, 2015 USD ($)	May. 31, 2015 USD ($)	[2]	Jun. 30, 2015 USD ($) asset_group $ / shares MW	Jun. 30, 2014 USD ($) $ / shares	Jun. 01, 2015 USD ($)	Dec. 31, 2014 USD ($)
Restructuring Cost and Reserve [Line Items]
TSA term of agreement					2 years
Goodwill	[1]	$ 470			$ 470			$ 72
Retail energy					554	$ 630
Income from continuing operations after income taxes					121	(56)
Net income		90	$ 32		$ 122	$ (53)
Earnings per share (in dollars per share) | $ / shares					$ 1.34	$ (0.63)
RJS Power
Restructuring Cost and Reserve [Line Items]
Goodwill							$ 398
Spinoff from PPL
Restructuring Cost and Reserve [Line Items]
Restructuring costs					$ 10
Spinoff | Spinoff from PPL
Restructuring Cost and Reserve [Line Items]
Amount of accrued liability for separation benefits		$ 2			$ 2			9
Number of asset groups that will be divested | asset_group					1
Number of asset groups proposed to be divested, one of which to be selected | asset_group					2
Talen Energy Supply
Restructuring Cost and Reserve [Line Items]
Accelerated stock based compensation and pro-rated stock-based compensation awards					$ 25
Goodwill								$ 72
Revenue Adjustment | Restatement Adjustment
Restructuring Cost and Reserve [Line Items]
Retail energy					(7)
Income from continuing operations after income taxes					(4)
Net income					$ (4)
Earnings per share (in dollars per share) | $ / shares					$ (0.04)
Minimum | Spinoff | Spinoff from PPL
Restructuring Cost and Reserve [Line Items]
Capacity, in total, to be divested in connection with the spinoff | MW					1,300
Maximum | Spinoff | Spinoff from PPL
Restructuring Cost and Reserve [Line Items]
Capacity, in total, to be divested in connection with the spinoff | MW					1,400

[1] There were no accumulated impairment losses related to goodwill.

[2] Represents Talen Energy Supply's predecessor member's equity balance and activity prior to the June 1, 2015 spinoff transaction.