Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2017	Jun. 30, 2016	Mar. 23, 2016	Jun. 30, 2017	Jun. 30, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities				$ 2,898	$ 4,553
Quantifying Misstatement in Current Year Financial Statements, Amount	$ (127)
Net Cash Provided by (Used in) Investing Activities				(3,980)	(10,877)
Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	1,074
Net Cash Provided by (Used in) Investing Activities	2,284
Exelon Generation Co L L C [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities				974	2,387
Quantifying Misstatement in Current Year Financial Statements, Amount	(320)
Net Cash Provided by (Used in) Investing Activities				(1,357)	(2,210)
Exelon Generation Co L L C [Member] | Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	420
Net Cash Provided by (Used in) Investing Activities	892
Commonwealth Edison Co [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities				788	1,128
Quantifying Misstatement in Current Year Financial Statements, Amount	91
Net Cash Provided by (Used in) Investing Activities				(1,166)	(1,313)
Commonwealth Edison Co [Member] | Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	236
Net Cash Provided by (Used in) Investing Activities	620
PECO Energy Co [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities				368	339
Quantifying Misstatement in Current Year Financial Statements, Amount	42
Net Cash Provided by (Used in) Investing Activities				(242)	(291)
PECO Energy Co [Member] | Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	106
Net Cash Provided by (Used in) Investing Activities	69
Baltimore Gas and Electric Company [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities				472	489
Quantifying Misstatement in Current Year Financial Statements, Amount	40
Net Cash Provided by (Used in) Investing Activities				(383)	(375)
Baltimore Gas and Electric Company [Member] | Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	208
Net Cash Provided by (Used in) Investing Activities	$ 221
Pepco Holdings LLC [Member] | Predecessor [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities			$ 264
Net Cash Provided by (Used in) Investing Activities			$ (343)
Pepco Holdings LLC [Member] | Successor [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities		$ 188		403
Net Cash Provided by (Used in) Investing Activities		$ (350)		(667)
Delmarva Power and Light Company [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities				194	220
Net Cash Provided by (Used in) Investing Activities				(191)	(180)
Atlantic City Electric Company [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities				77	208
Net Cash Provided by (Used in) Investing Activities				(173)	(160)
Potomac Electric Power Company [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities				129	365
Net Cash Provided by (Used in) Investing Activities				$ (293)	$ (307)