Supplemental Financial Information - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013	Mar. 31, 2015
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		$ 96	$ 220		$ (38)
Total equity method investments		112	50
Net investment in leases (b)		352	361
Total investments		639	544
Compensation-related accruals	[1]	1,014	832
Taxes accrued		293	305			$ 65
Interest accrued		915	240
Severance accrued		21	49
Other accrued expenses		133	113	[2]
Total accrued expenses		2,376	1,539
Antelope Valle [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid			170
Other accrued expenses			19		55
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		63	13
Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		23	9
Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		4	1
Sunnyside [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments			5
Trust for Benefit of Employees [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[4]	85	85
Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Available-for-sale Securities, Noncurrent		29	5
Cost Method Investments		55	37
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		82	(61)		(107)
Total equity method investments		89	28
Net investment in leases (b)	[5]	6	7
Total investments		210	104
Compensation-related accruals	[1]	547	447
Taxes accrued		186	248
Interest accrued		77	66
Severance accrued		11	33
Other accrued expenses		114	92	[2]
Total accrued expenses		935	886
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		63	13
Exelon Generation Co L L C [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		23	9
Exelon Generation Co L L C [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		3	1
Exelon Generation Co L L C [Member] | Sunnyside [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments			5
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]	31	27
Exelon Generation Co L L C [Member] | Other Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Available-for-sale Securities, Noncurrent		29	5
Cost Method Investments		55	37
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		34	78		(8)
Total equity method investments		6	6
Total investments		6	6
Compensation-related accruals	[1]	183	153
Taxes accrued		63	59
Interest accrued		443	102
Severance accrued		3	2
Other accrued expenses		14	15
Total accrued expenses		706	331
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[3]	6	6
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		(13)	0		13
Total equity method investments		8	8
Total investments		28	31
Compensation-related accruals	[1]	66	50
Taxes accrued		4	3
Interest accrued		35	33
Severance accrued		0	1
Other accrued expenses		4	4
Total accrued expenses		109	91
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]	20	23
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Change in capital expenditures not paid		(9)	25		$ 48
Total equity method investments		8	8
Total investments		12	12
Compensation-related accruals	[1]	57	58
Taxes accrued		23	42
Interest accrued		27	29
Severance accrued		1	2
Other accrued expenses		2	0
Total accrued expenses		110	131
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
Exelon Consolidations [Member]
Supplemental Balance Sheet Information [Line Items]
Net investment in leases (b)	[5]	$ 358	$ 367

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

[2] Includes $19 million for amounts accrued related to Antelope Valley as of December 31, 2014.

[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.

[5] Represents direct financing lease investments.