Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Average borrowings	$ 472	$ 531
Maximum borrowings outstanding	$ 890	$ 1,237
Short-term Debt, Weighted Average Interest Rate, over Time	2.25%	2.21%
Average interest rates at year end	2.25%	2.15%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Average borrowings	$ 13	$ 37
Maximum borrowings outstanding	$ 357	$ 583
Short-term Debt, Weighted Average Interest Rate, over Time	1.84%	1.96%
Average interest rates at year end	1.84%	1.96%
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 236	$ 154
Maximum borrowings outstanding	$ 465	$ 520
Short-term Debt, Weighted Average Interest Rate, over Time	2.38%	2.14%
Average interest rates at year end	2.38%	2.14%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 0	$ 68
Maximum borrowings outstanding	$ 21	$ 350
Short-term Debt, Weighted Average Interest Rate, over Time	2.39%	2.24%
Average interest rates at year end	2.39%	2.24%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 103	$ 65
Maximum borrowings outstanding	$ 298	$ 239
Short-term Debt, Weighted Average Interest Rate, over Time	2.46%	2.18%
Average interest rates at year end	2.46%	2.18%
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average borrowings	$ 3	$ 4
Maximum borrowings outstanding	$ 144	$ 95
Short-term Debt, Weighted Average Interest Rate, over Time	1.92%	1.93%
Average interest rates at year end	1.92%	1.93%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 45	$ 22
Maximum borrowings outstanding	$ 144	$ 90
Short-term Debt, Weighted Average Interest Rate, over Time	2.56%	2.24%
Average interest rates at year end	2.56%	2.24%
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 21	$ 87
Maximum borrowings outstanding	$ 125	$ 245
Short-term Debt, Weighted Average Interest Rate, over Time	2.02%	2.07%
Average interest rates at year end	2.02%	2.07%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 51	$ 95
Maximum borrowings outstanding	$ 180	$ 210
Short-term Debt, Weighted Average Interest Rate, over Time	2.43%	2.21%
Average interest rates at year end	2.43%	2.21%
Commercial Paper [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 870	$ 89
Average interest rates at year end	2.25%	2.15%
Commercial Paper [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 320	$ 0
Average interest rates at year end	1.84%	1.96%
Commercial Paper [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 130	$ 0
Average interest rates at year end	2.38%	2.14%
Commercial Paper [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 0
Average interest rates at year end	2.39%	2.24%
Commercial Paper [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 76	$ 35
Average interest rates at year end	2.46%	2.18%
Commercial Paper [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 136
Commercial Paper [Member] | Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Commercial Paper	208	$ 54
Commercial Paper [Member] | Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 82	$ 40
Average interest rates at year end	2.56%	2.24%
Commercial Paper [Member] | Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 56	$ 0
Average interest rates at year end	2.02%	2.07%
Commercial Paper [Member] | Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 70	$ 14
Average interest rates at year end	2.43%	2.21%