Segment Information - Reconciliation to Consolidated Financial Statements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 8,830	[1]	$ 7,237	[1]
Operating revenues from affiliates	1	[2]	1	[2]
Net income (loss)	738		93
Assets	87,391		86,814		86,814
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	5,840	[3]	4,390	[3]
Operating Segments [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues	5,840	[1],[4]	4,390	[1],[4]
Operating revenues from affiliates	210	[2],[4]	316	[2],[4]
Net income (loss)	485	[4]	(185)	[4]
Assets	45,318	[4]	45,348	[4]
Utility Taxes	27		24
Operating Segments [Member] | Commonwealth Edison Co [Member]
Segment Reporting Information [Line Items]
Revenues	1,185	[1]	1,134	[1]
Operating revenues from affiliates	1	[2]	1	[2]
Net income (loss)	90		98
Assets	25,731		25,392
Utility Taxes	62		63
Operating Segments [Member] | PECO Energy Co [Member]
Segment Reporting Information [Line Items]
Revenues	985	[1]	993	[1]
Operating revenues from affiliates	0	[2]	1	[2]
Net income (loss)	139		89
Assets	10,169		9,943
Utility Taxes	35		35
Operating Segments [Member] | Baltimore Gas and Electric Company [Member]
Segment Reporting Information [Line Items]
Revenues	1,036	[1]	1,054	[1]
Operating revenues from affiliates	7	[2]	16	[2]
Net income (loss)	109		88
Assets	8,130		8,078
Utility Taxes	52		20
Operating Segments [Member] | PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	63		88
Operating Segments [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	138		120
Operating Segments [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	9		108
Other Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	318	[1],[5]	290	[1],[5]
Operating revenues from affiliates	316	[2],[5]	290	[2],[5]
Net income (loss)	(84)	[5]	4	[5]
Assets	10,457	[5]	9,794	[5]
Intersegment Eliminations [Member] | Segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	(534)	[1]	(624)	[1]
Operating revenues from affiliates	(533)	[2]	(623)	[2]
Net income (loss)	(1)		(1)
Assets	(12,414)		(11,741)
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	$ 0		$ 0

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246M0JGQzRCODYwOEI3OTJGM0VFMzEwOTNBRjYwNTk1MjUM}

[2] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246NzEwQ0VGNzJGQTI1RkM2RDgzOUMwOTNBRjYwNUU2MTQM}

[3] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246MzJCOTc5NTI3RTkyMDA2QTkzQzgwOTNBRjYwNURBRkYM}

[4] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246NTk4QTIxQTlGRTU5OTQxMkFDM0QwOTNBRjYwNTMyMDIM}

[5] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVmN2Y3ZjVlMDU4YzQwMGVhOTA4ZWJkNWMzOGFmYjNhfFRleHRTZWxlY3Rpb246QzVGNDk1MTM4RDRDN0NDQjA5MkUwOTNBRjYwNUZCMzMM}