Acquisitions, Development and Divestitures (Anticipated Divestitures Discontinued Operations) (Details) $ in Millions		1 Months Ended	3 Months Ended			9 Months Ended
		Nov. 30, 2014 USD ($) facility MW	Mar. 31, 2016 USD ($) MW	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Components of Discontinued Operations
Income (Loss) from Discontinued Operations (net of income taxes)				$ (62)	$ 7	$ (61)	$ 10
Holtwood and Lake Wallenpaupack Hydroelectric Projects | Forecast | Disposal Group Held for Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase price of disposal group			$ 860
Capacity of facility sold | MW			308
Talen Ironwood Holdings, LLC | Forecast | Disposal Group Held for Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase price of disposal group			$ 654
Repayments of indebtedness			$ 41
Capacity of facility sold | MW			660
C.P. Crane, LLC | Forecast | Disposal Group Held for Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capacity of facility sold | MW			402
Sapphire
Components of Discontinued Operations
Operating revenues				36		44
Operating expenses				27		34
Impairment	[1]			109		109
Income (loss) before income taxes				(100)		(99)
Income tax expense				38		38
Income (Loss) from Discontinued Operations (net of income taxes)				$ (62)		$ (61)
Talen Montana Hydro Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capacity of facility sold | MW		633
Agreed upon sales price for disposal of hydroelectric facilities owned by PPL Montana		$ 900
Number of hydroelectric facilities owned by PPL Montana to be sold | facility		11
Components of Discontinued Operations
Operating revenues					33		103
Interest expense	[2]				2		6
Income (loss) before income taxes	[3]				11		20
Income (Loss) from Discontinued Operations (net of income taxes)	[3]				$ 7		$ 10

[1] See Notes 13 and 15 for additional information on this non-cash charge.

[2] Represents allocated interest expense based upon the discontinued operations share of the net assets of Talen Energy.

[3] Includes an impairment charge related to the Kerr Dam Project. See Note 13 for additional information on this non-cash charge.