Regulatory Matters Annual Electric Transmission Filings (Details) - USD ($)

1 Months Ended

3 Months Ended

6 Months Ended

12 Months Ended

Jul. 29, 2016

Nov. 06, 2015

Sep. 15, 2014

Mar. 31, 2013

Dec. 31, 2016

Sep. 30, 2016

Jun. 30, 2016

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2016

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 138

$ (50)

$ 269

Commonwealth Edison Co [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 90,000,000

$ 68,000,000

$ 36,000,000

Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint

11.50%

Public Utilities, Requested Equity Capital Structure, Percentage

8.47%

8.61%

8.62%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 4,000,000

$ 18,000,000

$ (14,000,000)

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 94,000,000

$ 86,000,000

$ 22,000,000

Public Utilities, Requested Return on Equity, Percentage

11.50%

Cap on Equity Component of Rate of Return on Common Equity in Federal Energy Regulatory Committee Complaint

55.00%

Baltimore Gas and Electric Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 12,000,000

$ 0

$ 9,000,000

Public Utilities, Requested Equity Capital Structure, Percentage

8.09%

8.46%

8.53%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 68,000,000

$ 99,000,000

$ 3,000,000

$ (3,000,000)

$ 5,000,000

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 28,000,000

$ 10,000,000

$ 17,000,000

Public Utilities, Requested Return on Equity, Percentage

10.50%

11.30%

Potomac Electric Power Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 2,000,000

$ 10,000,000

$ (9,000,000)

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

9.55%

Public Utilities, Approved Equity Capital Structure, Percentage

7.88%

8.36%

8.60%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ (10,000,000)

$ (3,000,000)

$ (1,000,000)

Public Utilities, Approved Rate Increase (Decrease), Amount

(23,000,000)

5,000,000

7,000,000

Current Year Revenue Adjustment

$ (15,000,000)

$ (2,000,000)

$ 17,000,000

Public Utilities, Requested Return on Equity, Percentage

10.50%

11.30%

Delmarva Power and Light Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 66,000,000

$ 8,000,000

$ 15,000,000

$ 4,000,000

Public Utilities, Approved Return on Equity, Percentage

0.00%

Public Utilities, Approved Equity Capital Structure, Percentage

7.21%

7.80%

8.05%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 57,000,000

$ (10,000,000)

$ (1,000,000)

$ 6,000,000

Public Utilities, Approved Rate Increase (Decrease), Amount

(14,000,000)

12,000,000

25,000,000

Current Year Revenue Adjustment

$ (12,000,000)

$ (2,000,000)

$ 15,000,000

Public Utilities, Requested Return on Equity, Percentage

10.50%

11.30%

Atlantic City Electric Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 8,000,000

$ 10,000,000

$ 4,000,000

Public Utilities, Approved Equity Capital Structure, Percentage

7.83%

8.51%

8.66%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ (14,000,000)

$ 2,000,000

$ 3,000,000

Public Utilities, Approved Rate Increase (Decrease), Amount

(6,000,000)

12,000,000

7,000,000

Current Year Revenue Adjustment

$ 0

Public Utilities, Requested Return on Equity, Percentage

10.50%

11.30%

Electric Distribution [Member] | Commonwealth Edison Co [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 134

$ 85

$ 160

Public Utilities, Approved Return on Equity, Percentage

8.59%

9.09%

9.20%

Public Utilities, Requested Equity Capital Structure, Percentage

6.71%

7.05%

7.06%

Public Utilities, Approved Equity Capital Structure, Percentage

6.69%

7.02%

7.04%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ (18,000,000)

$ 127

$ (67)

$ 232

Public Utilities, Approved Rate Increase (Decrease), Amount

$ (7)

$ (152)

$ 72

Public Utilities, Requested Return on Equity, Percentage

8.64%

9.14%

9.25%

Electric Distribution [Member] | Baltimore Gas and Electric Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 116,000,000

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 44,000,000

Public Utilities, Requested Return on Equity, Percentage

9.80%

Electric Distribution [Member] | Potomac Electric Power Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 53,000,000

$ 86,000,000

Public Utilities, Approved Return on Equity, Percentage

10.60%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 82,000,000

Electric Distribution [Member] | Delmarva Power and Light Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 39,000,000

63,000,000

$ 15,000,000

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

9.70%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 30,000,000

Electric Distribution [Member] | Atlantic City Electric Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 45,000,000