Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average borrowings	$ 1,125	$ 499	$ 571
Maximum borrowings outstanding	$ 3,076	$ 739	$ 1,164
Average interest rates, computed on a daily basis	0.88%	0.53%	0.32%
Average interest rates at year end	1.12%	0.88%	0.53%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Average borrowings	$ 536	$ 1	$ 93
Maximum borrowings outstanding	$ 1,735	$ 50	$ 552
Average interest rates, computed on a daily basis	0.94%	0.49%	0.32%
Average interest rates at year end	1.14%
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 256	$ 461	$ 415
Maximum borrowings outstanding	$ 755	$ 684	$ 597
Average interest rates, computed on a daily basis	0.77%	0.53%	0.33%
Average interest rates at year end		0.89%	0.50%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 143	$ 37	$ 64
Maximum borrowings outstanding	$ 369	$ 210	$ 180
Average interest rates, computed on a daily basis	0.77%	0.48%	0.29%
Average interest rates at year end	0.95%	0.87%	0.61%
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Average borrowings	$ 153	$ 444	$ 153
Maximum borrowings outstanding	$ 559	$ 784	$ 369
Average interest rates, computed on a daily basis	1.03%	0.90%	0.56%
Average interest rates at year end		1.22%	0.78%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 4	$ 34	$ 37
Maximum borrowings outstanding	$ 73	$ 190	$ 209
Average interest rates, computed on a daily basis	0.71%	0.44%	0.28%
Average interest rates at year end	0.90%	0.68%	0.46%
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 33	$ 81	$ 69
Maximum borrowings outstanding	$ 116	$ 179	$ 177
Average interest rates, computed on a daily basis	0.68%	0.47%	0.26%
Average interest rates at year end		0.79%	0.42%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 0	$ 175	$ 112
Maximum borrowings outstanding	$ 5	$ 253	$ 259
Average interest rates, computed on a daily basis	0.65%	0.46%	0.27%
Average interest rates at year end		0.65%	0.52%