Supplemental Financial Information Supplemental Financial Information - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 24, 2016	Mar. 23, 2016	Dec. 31, 2015
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		$ 1,349	$ 898	$ 635			$ 6,502
Restricted cash		247	207	253			205
Restricted cash included in other long-term assets		185	85	26			5
Total cash, cash equivalents and restricted cash		1,781	1,190	914			6,712
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	1,656	1,858
Allowance for uncollectible accounts	[2]	(319)	(322)
Purchased Receivables [Abstract]
Purchased receivables		313	298
Allowance for uncollectible accounts	[3]	(34)	(31)
Purchased receivables, net		279	267
Investments [Abstract]
Total equity method investments		267	297
Equity investments without readily determinable fair values		72	62
Other Investments		2
Total Investments		625	640
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	1,191	978
Taxes accrued		412	373
Interest accrued		334	328
Severance accrued		44	58
Other accrued expenses		131	100
Total accrued expenses		2,112	1,837
Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	14	14
Bloom Energy
Investments [Abstract]
Equity Method Investments		180	206
NET Power
Investments [Abstract]
Equity Method Investments		70	76
Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		3	1
Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	244	244
Other available for sale investments
Investments [Abstract]
Available for sale investments		40	37
Exelon Generation Co L L C [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		750	416	290			431
Restricted cash		153	138	158			123
Restricted cash included in other long-term assets		0	0	0			2
Total cash, cash equivalents and restricted cash		903	554	448			556
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	965	1,017
Allowance for uncollectible accounts	[2]	(104)	(114)
Investments [Abstract]
Total equity method investments		251	283
Equity investments without readily determinable fair values		72	62
Other Investments		2
Total Investments		414	433
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	479	407
Taxes accrued		226	444
Interest accrued		77	78
Severance accrued		26	30
Other accrued expenses		90	63
Total accrued expenses		898	1,022
Exelon Generation Co L L C [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Exelon Generation Co L L C [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		180	206
Exelon Generation Co L L C [Member] | NET Power
Investments [Abstract]
Equity Method Investments		70	76
Exelon Generation Co L L C [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		1	1
Exelon Generation Co L L C [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	49	51
Exelon Generation Co L L C [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		40	37
Commonwealth Edison Co [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		135	76	56			67
Restricted cash		29	5	2			2
Restricted cash included in other long-term assets		166	63	0			0
Total cash, cash equivalents and restricted cash		330	144	58			69
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	223	242
Allowance for uncollectible accounts	[2]	(81)	(73)
Purchased Receivables [Abstract]
Purchased receivables		94	87
Allowance for uncollectible accounts	[3]	(17)	(14)
Purchased receivables, net		77	73
Investments [Abstract]
Total equity method investments		6	6
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		6	6
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	187	158
Taxes accrued		71	60
Interest accrued		105	102
Severance accrued		2	2
Other accrued expenses		8	5
Total accrued expenses		373	327
Commonwealth Edison Co [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	6	6
Commonwealth Edison Co [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	0	0
Commonwealth Edison Co [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
PECO Energy Co [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		130	271	63			295
Restricted cash		5	4	4			3
Restricted cash included in other long-term assets		0	0	0			0
Total cash, cash equivalents and restricted cash		135	275	67			298
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	114	162
Allowance for uncollectible accounts	[2]	(61)	(56)
Purchased Receivables [Abstract]
Purchased receivables		74	70
Allowance for uncollectible accounts	[3]	(5)	(5)
Purchased receivables, net		69	65
Investments [Abstract]
Total equity method investments		8	8
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		25	25
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	49	64
Taxes accrued		28	15
Interest accrued		33	33
Severance accrued		0	0
Other accrued expenses		3	2
Total accrued expenses		113	114
PECO Energy Co [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	8	8
PECO Energy Co [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
PECO Energy Co [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
PECO Energy Co [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
PECO Energy Co [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	17	17
PECO Energy Co [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Baltimore Gas and Electric Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		7	17	23			9
Restricted cash		6	1	24			24
Restricted cash included in other long-term assets		0	0	3			3
Total cash, cash equivalents and restricted cash		13	18	50			36
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	168	205
Allowance for uncollectible accounts	[2]	(20)	(24)
Purchased Receivables [Abstract]
Purchased receivables		61	58
Allowance for uncollectible accounts	[3]	(3)	(3)
Purchased receivables, net		58	55
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		5	5
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	68	58
Taxes accrued		46	71
Interest accrued		39	34
Severance accrued		0	0
Other accrued expenses		2	1
Total accrued expenses		155	164
Baltimore Gas and Electric Company [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Baltimore Gas and Electric Company [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	5	5
Baltimore Gas and Electric Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Pepco Holdings LLC [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		124	30
Restricted cash		43	42
Restricted cash included in other long-term assets		19	23
Total cash, cash equivalents and restricted cash		186	95	236
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	186	232
Allowance for uncollectible accounts	[2]	(53)	(55)
Purchased Receivables [Abstract]
Purchased receivables		84	83
Allowance for uncollectible accounts	[3]	(9)	(9)
Purchased receivables, net		75	74
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		130	132
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	99	106
Taxes accrued		74	61
Interest accrued		50	48
Severance accrued		5	17
Other accrued expenses		28	29
Total accrued expenses		256	261
Pepco Holdings LLC [Member] | Successor [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents				170
Restricted cash				43
Restricted cash included in other long-term assets				23
Total cash, cash equivalents and restricted cash				236	$ 348
Pepco Holdings LLC [Member] | Predecessor [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents						$ 319	26
Restricted cash						11	14
Restricted cash included in other long-term assets						18	18
Total cash, cash equivalents and restricted cash						$ 348	58
Pepco Holdings LLC [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Pepco Holdings LLC [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	130	132
Pepco Holdings LLC [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Potomac Electric Power Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		16	5	9			5
Restricted cash		37	35	33			2
Restricted cash included in other long-term assets		0	0	0			0
Total cash, cash equivalents and restricted cash		53	40	42			7
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	97	133
Allowance for uncollectible accounts	[2]	(21)	(21)
Purchased Receivables [Abstract]
Purchased receivables		57	56
Allowance for uncollectible accounts	[3]	(5)	(5)
Purchased receivables, net		52	51
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		105	102
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	29	29
Taxes accrued		58	68
Interest accrued		25	23
Severance accrued		0	0
Other accrued expenses		14	17
Total accrued expenses		126	137
Potomac Electric Power Company [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Potomac Electric Power Company [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	105	102
Potomac Electric Power Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Delmarva Power & Light Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		23	2	46			5
Restricted cash		1	0	0			0
Restricted cash included in other long-term assets		0	0	0			0
Total cash, cash equivalents and restricted cash		24	2	46			5
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	59	68
Allowance for uncollectible accounts	[2]	(13)	(16)
Purchased Receivables [Abstract]
Purchased receivables		8	9
Allowance for uncollectible accounts	[3]	(1)	(1)
Purchased receivables, net		7	8
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		0	0
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	19	17
Taxes accrued		4	4
Interest accrued		8	8
Severance accrued		0	0
Other accrued expenses		8	6
Total accrued expenses		39	35
Delmarva Power & Light Company [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Delmarva Power & Light Company [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Delmarva Power & Light Company [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Delmarva Power & Light Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Delmarva Power & Light Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	0	0
Delmarva Power & Light Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Atlantic City Electric Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		7	2	101			3
Restricted cash		4	6	9			12
Restricted cash included in other long-term assets		19	23	23			18
Total cash, cash equivalents and restricted cash		30	31	$ 133			$ 33
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	30	31
Allowance for uncollectible accounts	[2]	(19)	(18)
Purchased Receivables [Abstract]
Purchased receivables		19	18
Allowance for uncollectible accounts	[3]	(3)	(3)
Purchased receivables, net		16	15
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		0	0
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	12	11
Taxes accrued		5	5
Interest accrued		12	12
Severance accrued		0	0
Other accrued expenses		6	5
Total accrued expenses		35	33
Atlantic City Electric Company [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Atlantic City Electric Company [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	0	0
Atlantic City Electric Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		$ 0	$ 0

[1] Represents unbilled portion of receivables estimated under Exelon’s unbilled critical accounting policy.

[2] Includes the estimated allowance for uncollectible accounts on billed customer and other accounts receivable.

[3] For ComEd, BGE, Pepco and DPL, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through a rate rider. BGE, Pepco and DPL recover actual write-offs which are reflected in the POR discount rate.

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

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

[6] The Registrants’ debt and equity security investments are recorded at fair market value.