Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues		$ 7,875	$ 9,002	$ 6,910	$ 7,573	$ 6,702	$ 7,401	$ 6,514	$ 8,830	$ 31,360	$ 29,447	$ 27,429
Operating revenues from affiliates										10	9	23
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues										6,179	5,900	5,259
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues										4,412	4,710	4,475
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues										1,769	2,212	1,422
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues										1,156	985	843
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues										837	857	935
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[1]									907	1,102	1,309
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues										15,260	15,766	14,243
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									2,491	3,369	3,150
Derivative, Loss on Derivative										(41)		(591)
Derivative, Gain on Derivative											257
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues										17,751	19,135	17,393
Scenario, Adjustment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates											(284)
Scenario, Adjustment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates											284
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									6,212	5,974	5,414
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									4,402	4,712	4,488
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,778	2,217	1,468
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,198	996	846
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									831	863	938
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3]									969	1,182	1,379
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									15,390	15,944	14,533
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2],[3]									2,361	3,191	2,860
Amortization of intangible assets related to commodity contracts										52	7	289
Derivative, Loss on Derivative										(500)		(174)
Derivative, Gain on Derivative											203
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									17,751	19,135	17,393
Operating Segments [Member] | Scenario, Adjustment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues											284
Operating Segments [Member] | Scenario, Adjustment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues											(284)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[4]									5	5	6
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(33)	(74)	(155)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										10	(2)	(13)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(9)	(5)	(46)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(42)	(11)	(3)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										6	(6)	(3)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]									(62)	(80)	(70)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(130)	(178)	(290)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[2]									130	178	290
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										$ 0	$ 0	$ 0

[1] (b)Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants

[2] (c)Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $52 million decrease to revenues, a $7 million increase to revenues, and a $289 million decrease to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2016, 2015, and 2014, respectively, unrealized mark-to-market losses of $500 million, gains of $203 million, and losses of $174 million for the years ended December 31, 2016, 2015, and 2014, respectively, and elimination of intersegment revenues.

[3] (a)On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenues are included on a fully consolidated basis.

[4] Amounts included represent activity for PHI's successor period, March 24, 2016 through December 31, 2016. PHI includes the three reportable segments: Pepco, DPL and ACE. See tables below for PHI's predecessor periods, including Pepco, DPL and ACE, for January 1, 2016 to March 23, 2016 and for the years ended December 31, 2015