Derivative Financial Instruments - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended									9 Months Ended		9 Months Ended											9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended		9 Months Ended										3 Months Ended		9 Months Ended
	Sep. 30, 2014		Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Designated as Hedging Instrument [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member] GWh	Sep. 30, 2013 Exelon Generation Co L L C [Member] GWh	Sep. 30, 2014 Exelon Generation Co L L C [Member] GWh	Sep. 30, 2013 Exelon Generation Co L L C [Member] GWh	Dec. 31, 2013 Exelon Generation Co L L C [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member] Derivative [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Derivative [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Commonwealth Edison Co [Member]	Dec. 31, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2014 PECO Energy Co [Member]	Sep. 30, 2014 Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Minimum [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Minimum [Member] Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Maximum [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Maximum [Member] Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Interest Rate Swap [Member] Derivative [Member]	Sep. 30, 2014 Interest Rate Swap [Member] Exelon Generation Co L L C [Member]	Feb. 06, 2014 Interest Rate Swap [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Interest Rate Swap [Member] Exelon Generation Co L L C [Member] Derivative [Member]	Sep. 30, 2014 Interest Rate Swap [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Interest Rate Contract [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Foreign Exchange Contract [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Fair Value Hedging [Member] Interest Rate Swap [Member] Designated as Hedging Instrument [Member]	Dec. 31, 2013 Fair Value Hedging [Member] Interest Rate Swap [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Fair Value Hedging [Member] Interest Rate Swap [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Dec. 31, 2013 Fair Value Hedging [Member] Interest Rate Swap [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Cash Flow Hedging [Member] Interest Rate Contract [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Cash Flow Hedging [Member] Interest Rate Contract [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Antelope Valle [Member] Cash Flow Hedging [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Other Solar Projects [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Other Solar Projects [Member] Exelon Generation Co L L C [Member] Derivative [Member]	Sep. 30, 2014 Other Solar Projects [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Other Solar Projects [Member] Cash Flow Hedging [Member] Interest Rate Contract [Member] Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 PHI Merger [Member]	Sep. 30, 2014 PHI Merger [Member] Interest Rate Swap [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 ExGen Texas Power [Member] Interest Rate Swap [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 ExGen Texas Power [Member] Cash Flow Hedging [Member] Interest Rate Contract [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2014 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Sep. 30, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Sep. 30, 2014 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Sep. 30, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] Reclassification out of Accumulated Other Comprehensive Income [Member]	Sep. 30, 2014 Commonwealth Edison Co Affiliate [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 PECO Energy Co Affiliate [Member] PECO Energy Co [Member]	Sep. 30, 2014 Baltimore Gas And Electric Company Affiliate [Member] Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Hypothetical Increase In Interest Rates			0.50%
Expected Generation Hedged In Next Twelve Months																			98.00%		101.00%
Expected Generation Hedged In Year Two																			86.00%		89.00%
Expected generation hedged in year three																			55.00%		58.00%
Estimated percentage of natural gas purchases hedged																	30.00%			10.00%		20.00%
Proprietary trading activities volume						3,006	2,499	8,129	6,066
Derivative, Notional Amount																							$ 1,600		$ 240	$ 700	$ 150	$ 97	$ 322	$ 1,450	$ 1,275											$ 1,250	$ 505
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives					2,431								781																					400
Hypothetical increase in interest rates associated with variable-rate debt			7
Increase In Notional Amount Of Derivative Instruments																														100					222
Increase In Notional Amount Of Derivative Instruments1																														75
Interest rate swaps previously held by acquiree																																550	550
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments																														24	26	12	23
Ineffective portion recognized in income	6	[1]	14
DOE interest rate swap																																				485
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)						21
Notional amounts on forward starting interest rate swaps																																					28		26
Mark-to-market derivative liabilities (noncurrent liabilities)	291		291	300		104		104		120					164	176																		10				2			9			3
Interest Rate Derivative Assets Noncurrent	30		30	38		13		13		31	3	3	13	26																										1
Derivative Liability, Current	249		249	159		235		235		142					14	17								1
Cash collateral received not offset against net derivative positions						43		43		10
Credit exposure under natural gas supply and management agreements																	6
Cash collateral posted	94		94			669		669		72
Letters of credit held						12		12		34
Net receivable from electric utility																																																	11
Net receivable from affiliated electric and gas utility																																																		21	34
Cash Flow Hedge Gain Loss Reclassified To Pretax Net Income From Accumulated Other Comprehensive Income						28	84	130	543																																				28	84	130	324
Expected reclassification from accumulated other comprehensive income to results of operations								67
Total																		23
Letters of credit posted	4		4			389		389		364
Cash collateral held						169		169		206					19
Incremental collateral for loss of investment grade credit rating						2,100		2,100		2,000							25	47
Interest Rate Fair Value Hedge Asset at Fair Value	2		2			8		8
Counter Party With Exposure	$ 2		$ 2

[1] For the three and nine months ended September 30, 2014, the loss on Generation swaps included $4 million and $12 million realized in earnings, respectively, with $2 million amount excluded from hedge effectiveness testing.