Business and Basis of Presentation (Details) $ / shares in Units, $ in Millions	3 Months Ended		4 Months Ended	5 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2014 USD ($) $ / shares	Sep. 30, 2015 USD ($)	May. 31, 2015 USD ($)	[1]	Sep. 30, 2015 USD ($) asset_group $ / shares MW	Sep. 30, 2014 USD ($) $ / shares	Dec. 31, 2014 USD ($)
Restructuring Cost and Reserve [Line Items]
TSA term of agreement						2 years
Increase (decrease) to retail energy	$ 277	$ 283				$ 831	$ 913
Energy-related businesses	156	189				404	469
Income (Loss) from Continuing Operations Before Income Taxes	(300)	168				(169)	54
Income from continuing operations after income taxes	(339)	94				(218)	38
Net income (loss)	$ (401)	$ 101	$ (311)	$ 32		$ (279)	$ 48
Earnings per share (in dollars per share) | $ / shares	$ (3.12)	$ 1.21				$ (2.69)	$ 0.57
Restatement adjustment | Revenue Adjustment for Affiliate Payable
Restructuring Cost and Reserve [Line Items]
Increase (decrease) to retail energy						$ (7)
Income from continuing operations after income taxes						(4)
Net income (loss)						$ (4)
Earnings per share (in dollars per share) | $ / shares						$ (0.03)
Restatement adjustment | Revenue Adjustment Related to Timing of Revenue Recognition
Restructuring Cost and Reserve [Line Items]
Energy-related businesses		$ 14					$ 17
Energy-related businesses, net of taxes		9					11
Income (Loss) from Continuing Operations Before Income Taxes		14					7
Income from continuing operations after income taxes		9					11
Net income (loss)		$ 9					$ 11
Earnings per share (in dollars per share) | $ / shares		$ 0.11					$ 0.13
PPL Corporation and Topaz Power Management, LP
Restructuring Cost and Reserve [Line Items]
Services provided under TSA	$ 9					$ 14
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								$ 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
Spinoff | Spinoff from PPL | Minimum
Restructuring Cost and Reserve [Line Items]
Capacity, in total, to be divested in connection with the spinoff | MW						1,300
Spinoff | Spinoff from PPL | Maximum
Restructuring Cost and Reserve [Line Items]
Capacity, in total, to be divested in connection with the spinoff | MW						1,400
Talen Energy Supply
Restructuring Cost and Reserve [Line Items]
Accelerated stock based compensation and pro-rated stock-based compensation awards						$ 25
Increase (decrease) to retail energy	277	$ 283				831	$ 913
Energy-related businesses	156	189				404	469
Income (Loss) from Continuing Operations Before Income Taxes	(300)	168				(169)	54
Income from continuing operations after income taxes	(339)	94				(218)	38
Net income (loss)	$ (401)	$ 101				$ (279)	$ 48

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