Supplemental Financial Information - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		$ 311	$ 112
Net investment in leases(b)	[1]		358
Investments		629	639
Compensation-related accruals	[2]	1,199	1,014
Taxes accrued		723	293
Interest accrued		1,234	915
Severance accrued		44	21
Other accrued expenses		260	133
Total accrued expenses		3,460	2,376
Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	22	22
Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		216	63
Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		57	23
Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		16	4
Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	232	85
Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		52	55
Other available for sale investments		34	29
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		288	89
Net investment in leases(b)	[1]		6
Investments		418	210
Compensation-related accruals	[2]	557	547
Taxes accrued		239	186
Interest accrued		82	77
Severance accrued		15	11
Other accrued expenses		96	114
Total accrued expenses		989	935
Exelon Generation Co L L C [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	0	0
Exelon Generation Co L L C [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		216	63
Exelon Generation Co L L C [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		57	23
Exelon Generation Co L L C [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		15	3
Exelon Generation Co L L C [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	44	31
Exelon Generation Co L L C [Member] | Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		52	55
Other available for sale investments		34	29
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		6	6
Investments		6	6
Compensation-related accruals	[2]	199	183
Taxes accrued		330	63
Interest accrued		609	443
Severance accrued		2	3
Other accrued expenses		110	14
Total accrued expenses		1,250	706
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	6	6
Commonwealth Edison Co [Member] | Malacha [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments			0
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		8	8
Investments		25	28
Compensation-related accruals	[2]	67	66
Taxes accrued		4	4
Interest accrued		30	35
Severance accrued		0	0
Other accrued expenses		3	4
Total accrued expenses		104	109
PECO Energy Co [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	8	8
PECO Energy Co [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	17	20
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		8	8
Investments		12	12
Compensation-related accruals	[2]	64	57
Taxes accrued		78	23
Interest accrued		31	27
Severance accrued		0	1
Other accrued expenses		2	2
Total accrued expenses		175	110
Baltimore Gas and Electric Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	8	8
Baltimore Gas and Electric Company [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	4	4
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0
Investments		133
Compensation-related accruals	[2]	112
Taxes accrued		65
Interest accrued		49
Severance accrued		19
Other accrued expenses		27
Total accrued expenses		272
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments			0
Investments			80
Compensation-related accruals	[2]		88
Taxes accrued			77
Interest accrued			54
Severance accrued			0
Other accrued expenses			47
Total accrued expenses			266
Pepco Holdings LLC [Member] | Financing Trusts [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	0
Pepco Holdings LLC [Member] | Financing Trusts [Member] | Predecessor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]		0
Pepco Holdings LLC [Member] | Bloom Energy [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0
Pepco Holdings LLC [Member] | Bloom Energy [Member] | Predecessor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments			0
Pepco Holdings LLC [Member] | Net Power [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0
Pepco Holdings LLC [Member] | Net Power [Member] | Predecessor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments			0
Pepco Holdings LLC [Member] | Other Equity Method Investments [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0
Pepco Holdings LLC [Member] | Other Equity Method Investments [Member] | Predecessor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments			0
Pepco Holdings LLC [Member] | Trust for Benefit of Employees [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		133
Pepco Holdings LLC [Member] | Trust for Benefit of Employees [Member] | Predecessor [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments			80
Pepco Holdings LLC [Member] | Other Investments [Member] | Predecessor [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments			0
Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0	0
Investments		102	68
Compensation-related accruals	[2]	30	26
Taxes accrued		48	56
Interest accrued		21	23
Severance accrued		0	0
Other accrued expenses		14	14
Total accrued expenses		113	119
Potomac Electric Power Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	0	0
Potomac Electric Power Company [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments			68
Other available for sale investments		102
Potomac Electric Power Company [Member] | Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments			0
Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0	0
Investments		0	0
Compensation-related accruals	[2]	17	14
Taxes accrued		4	3
Interest accrued		8	8
Severance accrued		0	0
Other accrued expenses		7	6
Total accrued expenses		36	31
Delmarva Power and Light Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	0	0
Delmarva Power and Light Company [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Delmarva Power and Light Company [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Delmarva Power and Light Company [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Delmarva Power and Light Company [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments			0
Other available for sale investments		0
Delmarva Power and Light Company [Member] | Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments			0
Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0	0
Investments		0	0
Compensation-related accruals	[2]	11	8
Taxes accrued		9	23
Interest accrued		12	13
Severance accrued		0	0
Other accrued expenses		6	26
Total accrued expenses		38	70
Atlantic City Electric Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	0	0
Atlantic City Electric Company [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments			0
Other available for sale investments		$ 0
Atlantic City Electric Company [Member] | Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments			$ 0

[1] Represents direct financing lease investments.

[2] Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.

[3] Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments on the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information.

[4] (c)The Registrants’ investments in these marketable securities are recorded at fair market value.