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Segment Information - Electric and Gas Revenue by Customer Class (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Revenue, Major Customer [Line Items]        
Revenues $ 8,910 $ 8,853 $ 26,715 $ 24,925
Revenue from Related Parties 0 1 0 4
Commonwealth Edison Co [Member]        
Revenue, Major Customer [Line Items]        
Revenues 1,789 1,643 4,840 4,499
Revenue from Related Parties 9 15 19 31
Commonwealth Edison Co [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenues 1,815 1,678 4,784 4,540
Commonwealth Edison Co [Member] | Other Regulated Revenue [Member]        
Revenue, Major Customer [Line Items]        
Revenues (26) (35) 56 (41)
PECO Energy Co [Member]        
Revenue, Major Customer [Line Items]        
Revenues 818 813 2,399 2,306
Revenue from Related Parties 2 3 6 7
PECO Energy Co [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenues 813 808 2,377 2,293
PECO Energy Co [Member] | Other Regulated Revenue [Member]        
Revenue, Major Customer [Line Items]        
Revenues 5 5 22 13
Baltimore Gas and Electric Company [Member]        
Revenue, Major Customer [Line Items]        
Revenues 770 731 2,426 2,284
Revenue from Related Parties 7 6 20 16
Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenues 790 740 2,434 2,290
Baltimore Gas and Electric Company [Member] | Other Regulated Revenue [Member]        
Revenue, Major Customer [Line Items]        
Revenues (20) (9) (8) (6)
Pepco Holdings LLC [Member]        
Revenue, Major Customer [Line Items]        
Revenues 1,470 1,368 3,854 3,554
Revenue from Related Parties 3 6 10 13
Pepco Holdings LLC [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenues 1,462 1,337 3,757 3,567
Pepco Holdings LLC [Member] | Other Regulated Revenue [Member]        
Revenue, Major Customer [Line Items]        
Revenues 8 31 97 (13)
Potomac Electric Power Company [Member]        
Revenue, Major Customer [Line Items]        
Revenues 660 611 1,736 1,650
Revenue from Related Parties 2 3 4 6
Potomac Electric Power Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenues 650 593 1,680 1,629
Potomac Electric Power Company [Member] | Other Regulated Revenue [Member]        
Revenue, Major Customer [Line Items]        
Revenues 10 18 56 21
Delmarva Power and Light Company [Member]        
Revenue, Major Customer [Line Items]        
Revenues 360 337 1,040 954
Revenue from Related Parties 2 3 6 7
Delmarva Power and Light Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenues 361 329 1,022 968
Delmarva Power and Light Company [Member] | Other Regulated Revenue [Member]        
Revenue, Major Customer [Line Items]        
Revenues (1) 8 18 (14)
Atlantic City Electric Company [Member]        
Revenue, Major Customer [Line Items]        
Revenues 451 420 1,080 952
Revenue from Related Parties 1 1 2 3
Atlantic City Electric Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenues 451 415 1,057 972
Atlantic City Electric Company [Member] | Other Regulated Revenue [Member]        
Revenue, Major Customer [Line Items]        
Revenues 0 5 23 (20)
Rate-regulated electric revenues [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 4,657 4,365 12,432 11,585
Rate-regulated electric revenues [Member] | Commonwealth Edison Co [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 1,812 1,666 4,789 4,519
Rate-regulated electric revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 1,815 1,678 4,784 4,540
Revenue from Related Parties 9 15 19 31
Rate-regulated electric revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 6 3 24 10
Rate-regulated electric revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 978 920 2,479 2,389
Rate-regulated electric revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 433 379 1,176 1,067
Rate-regulated electric revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 148 135 420 388
Rate-regulated electric revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 11 10 33 33
Rate-regulated electric revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 245 234 676 663
Rate-regulated electric revenues [Member] | PECO Energy Co [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 757 751 2,008 1,931
Rate-regulated electric revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 757 753 2,011 1,934
Revenue from Related Parties 2 3 5 6
Rate-regulated electric revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 2 0 2 3
Rate-regulated electric revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 509 518 1,325 1,277
Rate-regulated electric revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 113 104 312 291
Rate-regulated electric revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 67 66 183 174
Rate-regulated electric revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 7 7 24 21
Rate-regulated electric revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 61 58 167 171
Rate-regulated electric revenues [Member] | Baltimore Gas and Electric Company [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 694 649 1,874 1,775
Rate-regulated electric revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 695 652 1,877 1,781
Revenue from Related Parties 4 3 10 9
Rate-regulated electric revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 3 0 7 3
Rate-regulated electric revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 383 389 1,044 1,034
Rate-regulated electric revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 73 65 202 183
Rate-regulated electric revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 128 113 342 311
Rate-regulated electric revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 7 7 20 20
Rate-regulated electric revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 104 78 269 233
Rate-regulated electric revenues [Member] | Pepco Holdings LLC [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 1,438 1,308 3,632 3,440
Rate-regulated electric revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 1,439 1,314 3,639 3,451
Revenue from Related Parties 3 6 10 13
Rate-regulated electric revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 2 0 3 2
Rate-regulated electric revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 782 763 1,924 1,825
Rate-regulated electric revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 150 134 392 355
Rate-regulated electric revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 320 262 825 755
Rate-regulated electric revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 15 14 45 45
Rate-regulated electric revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 172 141 453 471
Rate-regulated electric revenues [Member] | Potomac Electric Power Company [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 649 590 1,678 1,624
Rate-regulated electric revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 650 593 1,680 1,629
Revenue from Related Parties 2 3 4 6
Rate-regulated electric revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 1 0 2 1
Rate-regulated electric revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 309 307 785 779
Rate-regulated electric revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 36 36 101 101
Rate-regulated electric revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 244 195 616 558
Rate-regulated electric revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 8 8 24 25
Rate-regulated electric revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 53 47 154 166
Rate-regulated electric revenues [Member] | Delmarva Power and Light Company [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 337 303 899 846
Rate-regulated electric revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 338 306 904 852
Revenue from Related Parties 2 3 6 7
Rate-regulated electric revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 1 0 1 1
Rate-regulated electric revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 198 193 535 501
Rate-regulated electric revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 53 45 145 127
Rate-regulated electric revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 27 21 70 66
Rate-regulated electric revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 4 3 11 10
Rate-regulated electric revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 56 44 143 148
Rate-regulated electric revenues [Member] | Atlantic City Electric Company [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 450 414 1,055 969
Rate-regulated electric revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 451 415 1,057 972
Revenue from Related Parties 1 1 2 3
Rate-regulated electric revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated electric revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 275 263 604 545
Rate-regulated electric revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 61 53 146 127
Rate-regulated electric revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 49 46 139 131
Rate-regulated electric revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Public Authorities & Electric Railroads [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 3 3 10 10
Rate-regulated electric revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 63 50 158 159
Rate-regulated natural gas revenues [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 169 159 1,035 990
Rate-regulated natural gas revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Transportation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | PECO Energy Co [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 56 54 365 358
Rate-regulated natural gas revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 56 55 366 359
Revenue from Related Parties 0 0 1 1
Rate-regulated natural gas revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 36 32 251 252
Rate-regulated natural gas revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 13 16 94 86
Rate-regulated natural gas revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Transportation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 5 6 17 18
Rate-regulated natural gas revenues [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 2 1 4 3
Rate-regulated natural gas revenues [Member] | Baltimore Gas and Electric Company [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 93 85 549 503
Rate-regulated natural gas revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 95 88 557 509
Revenue from Related Parties 3 3 10 7
Rate-regulated natural gas revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 1 0 2 1
Rate-regulated natural gas revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 57 55 354 342
Rate-regulated natural gas revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 10 9 59 55
Rate-regulated natural gas revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 22 21 103 96
Rate-regulated natural gas revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Transportation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 6 3 41 16
Rate-regulated natural gas revenues [Member] | Pepco Holdings LLC [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 23 23 118 116
Rate-regulated natural gas revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 23 23 118 116
Rate-regulated natural gas revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 10 11 67 68
Rate-regulated natural gas revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 5 6 29 30
Rate-regulated natural gas revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 2 1 5 3
Rate-regulated natural gas revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Transportation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 3 3 11 10
Rate-regulated natural gas revenues [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 3 2 6 5
Rate-regulated natural gas revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Transportation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Delmarva Power and Light Company [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 23 23 118 116
Rate-regulated natural gas revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 23 23 118 116
Rate-regulated natural gas revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 10 11 67 68
Rate-regulated natural gas revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 5 6 29 30
Rate-regulated natural gas revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 2 1 5 3
Rate-regulated natural gas revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Transportation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 3 3 11 10
Rate-regulated natural gas revenues [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 3 2 6 5
Rate-regulated natural gas revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Residential [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Small Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Large Commercial & Industrial [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Transportation [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Rate-regulated natural gas revenues [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Other [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 0 0 0 0
Alternative revenue programs [Member] | Commonwealth Edison Co [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax (32) (38) 32 (51)
Alternative revenue programs [Member] | PECO Energy Co [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 3 5 20 10
Alternative revenue programs [Member] | Baltimore Gas and Electric Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax (24) (9) (17) (10)
Alternative revenue programs [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 6 31 94 (15)
Alternative revenue programs [Member] | Potomac Electric Power Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax 9 18 54 20
Alternative revenue programs [Member] | Delmarva Power and Light Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax (2) 8 17 (15)
Alternative revenue programs [Member] | Atlantic City Electric Company [Member] | Regulated Operation [Member] | Operating Segment [Member]        
Revenue, Major Customer [Line Items]        
Revenue from Contract with Customer, Including Assessed Tax $ 0 $ 5 $ 23 $ (20)