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Schedule II - Valuation and Qualifying Accounts Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 23, 2016 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Allowance for Uncollectible Accounts [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period | [1] | $ 284 |  | $ 322 |  | $ 334 | $ 284 |
Charged to Costs and Expenses | [1] |  |  | 159 |  | 126 | 162 |
Charged to Other Accounts | [1],[2] |  |  | 35 |  | 27 | 99 | [3]
Deductions | [1],[4] |  |  | 197 |  | 165 | 211 |
Balance at End of Period | [1] |  | $ 334 | 319 |  | 322 | 334 |
Deferred Tax Valuation Allowance [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 13 |  | 37 |  | 20 | 13 |
Charged to Costs and Expenses |  |  |  | 0 |  | 0 | 0 |
Charged to Other Accounts |  |  |  | 5 |  | 17 | 10 | [3]
Deductions |  |  |  | 7 |  | 0 | 3 |
Balance at End of Period |  |  | 20 | 35 |  | 37 | 20 |
Reserve for Obsolete Materials [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 105 |  | 174 |  | 113 | 105 |
Charged to Costs and Expenses |  |  |  | 25 |  | 56 | 12 |
Charged to Other Accounts |  |  |  | (31) | [5] | 10 | 1 | [3]
Deductions |  |  |  | 12 |  | 5 | 5 |
Balance at End of Period |  |  | 113 | 156 |  | 174 | 113 |
Exelon Generation Co L L C [Member] | Allowance for Uncollectible Accounts [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 77 |  | 114 |  | 91 | 77 |
Charged to Costs and Expenses |  |  |  | 44 |  | 34 | 19 |
Charged to Other Accounts |  |  |  | 4 |  | 0 | 3 |
Deductions |  |  |  | 58 |  | 11 | 8 |
Balance at End of Period |  |  | 91 | 104 |  | 114 | 91 |
Exelon Generation Co L L C [Member] | Deferred Tax Valuation Allowance [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 11 |  | 23 |  | 9 | 11 |
Charged to Costs and Expenses |  |  |  | 0 |  | 0 | 0 |
Charged to Other Accounts |  |  |  | 3 |  | 14 | 0 |
Deductions |  |  |  | 0 |  | 0 | 2 |
Balance at End of Period |  |  | 9 | 26 |  | 23 | 9 |
Exelon Generation Co L L C [Member] | Reserve for Obsolete Materials [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 102 |  | 166 |  | 106 | 102 |
Charged to Costs and Expenses |  |  |  | 20 |  | 51 | 6 |
Charged to Other Accounts |  |  |  | (32) | [6] | 9 | 0 |
Deductions |  |  |  | 9 |  | 0 | 2 |
Balance at End of Period |  |  | 106 | 145 |  | 166 | 106 |
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 75 |  | 73 |  | 70 | 75 |
Charged to Costs and Expenses |  |  |  | 44 |  | 39 | 45 |
Charged to Other Accounts | [7] |  |  | 23 |  | 20 | 23 |
Deductions | [8] |  |  | 59 |  | 56 | 73 |
Balance at End of Period |  |  | 70 | 81 |  | 73 | 70 |
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 3 |  | 5 |  | 4 | 3 |
Charged to Costs and Expenses |  |  |  | 3 |  | 3 | 4 |
Charged to Other Accounts |  |  |  | 1 |  | 1 | 1 |
Deductions |  |  |  | 3 |  | 3 | 4 |
Balance at End of Period |  |  | 4 | 6 |  | 5 | 4 |
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period | [9] | 83 |  | 56 |  | 61 | 83 |
Charged to Costs and Expenses | [9] |  |  | 33 |  | 26 | 32 |
Charged to Other Accounts | [9],[10] |  |  | 3 |  | 4 | 7 |
Deductions | [9],[11] |  |  | 31 |  | 35 | 61 |
Balance at End of Period | [9] |  | 61 | 61 |  | 56 | 61 |
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 1 |  | 2 |  | 2 | 1 |
Charged to Costs and Expenses |  |  |  | 0 |  | 0 | 1 |
Charged to Other Accounts |  |  |  | 0 |  | 0 | 0 |
Deductions |  |  |  | 0 |  | 0 | 0 |
Balance at End of Period |  |  | 2 | 2 |  | 2 | 2 |
PECO Energy Co [Member] | Allowance for Doubtful Accounts, Noncurrent [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  |  |  | 15 |  | 23 |  |
Balance at End of Period |  |  | 23 | 13 |  | 15 | 23 |
Baltimore Gas and Electric Company [Member] | Allowance for Uncollectible Accounts [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 49 |  | 24 |  | 32 | 49 |
Charged to Costs and Expenses |  |  |  | 10 |  | 8 | 1 |
Charged to Other Accounts |  |  |  | (2) |  | (3) | 9 |
Deductions | [12] |  |  | 12 |  | 13 | 27 |
Balance at End of Period |  |  | 32 | 20 |  | 24 | 32 |
Baltimore Gas and Electric Company [Member] | Deferred Tax Valuation Allowance [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 1 |  | 1 |  | 1 | 1 |
Charged to Costs and Expenses |  |  |  | 0 |  | 0 | 0 |
Charged to Other Accounts |  |  |  | 0 |  | 0 | 0 |
Deductions |  |  |  | 0 |  | 0 | 0 |
Balance at End of Period |  |  | 1 | 1 |  | 1 | 1 |
Baltimore Gas and Electric Company [Member] | Reserve for Obsolete Materials [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 0 |  | 0 |  | 0 | 0 |
Charged to Costs and Expenses |  |  |  | 1 |  | 0 | 0 |
Charged to Other Accounts |  |  |  | 0 |  | 0 | 0 |
Deductions |  |  |  | 0 |  | 0 | 0 |
Balance at End of Period |  |  | 0 | 1 |  | 0 | 0 |
Pepco Holdings LLC [Member] | Allowance for Uncollectible Accounts [Member] | Successor [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  |  | 52 | 55 |  | 80 |  |
Charged to Costs and Expenses |  |  | 65 | 28 |  | 19 |  |
Charged to Other Accounts | [13] |  | 5 | 7 |  | 6 |  |
Deductions | [14] |  | 42 | 37 |  | 50 |  |
Balance at End of Period |  | 52 | 80 | 53 |  | 55 | 80 |
Pepco Holdings LLC [Member] | Allowance for Uncollectible Accounts [Member] | Predecessor [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 56 | 52 |  |  |  | 56 |
Charged to Costs and Expenses |  | 16 |  |  |  |  |  |
Charged to Other Accounts | [13] | 2 |  |  |  |  |  |
Deductions | [14] | 22 |  |  |  |  |  |
Balance at End of Period |  | 52 |  |  |  |  |  |
Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member] | Successor [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  |  | 63 | 13 |  | 10 |  |
Charged to Costs and Expenses |  |  | 0 | 0 |  | 0 |  |
Charged to Other Accounts |  |  | (53) | 2 |  | 3 |  |
Deductions |  |  | 0 | 7 |  | 0 |  |
Balance at End of Period |  | 63 | 10 | 8 |  | 13 | 10 |
Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member] | Predecessor [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 63 | 63 |  |  |  | 63 |
Charged to Costs and Expenses |  | 0 |  |  |  |  |  |
Charged to Other Accounts |  | 0 |  |  |  |  |  |
Deductions |  | 0 |  |  |  |  |  |
Balance at End of Period |  | 63 |  |  |  |  |  |
Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member] | Successor [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  |  | 0 | 2 |  | 2 |  |
Charged to Costs and Expenses |  |  | 1 | 0 |  | 2 |  |
Charged to Other Accounts |  |  | 0 | 0 |  | 0 |  |
Deductions |  |  | (1) | 0 |  | 2 |  |
Balance at End of Period |  | 0 | 2 | 2 |  | 2 | 2 |
Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member] | Predecessor [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 0 | 0 |  |  |  | 0 |
Charged to Costs and Expenses |  | 0 |  |  |  |  |  |
Charged to Other Accounts |  | 0 |  |  |  |  |  |
Deductions |  | 0 |  |  |  |  |  |
Balance at End of Period |  | 0 |  |  |  |  |  |
Potomac Electric Power Company [Member] | Allowance for Uncollectible Accounts [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 17 |  | 21 |  | 29 | 17 |
Charged to Costs and Expenses |  |  |  | 11 |  | 8 | 29 |
Charged to Other Accounts | [15] |  |  | 3 |  | 2 | 3 |
Deductions | [16] |  |  | 14 |  | 18 | 20 |
Balance at End of Period |  |  | 29 | 21 |  | 21 | 29 |
Potomac Electric Power Company [Member] | Reserve for Obsolete Materials [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 0 |  | 1 |  | 1 | 0 |
Charged to Costs and Expenses |  |  |  | 0 |  | 1 | 3 |
Charged to Other Accounts |  |  |  | 0 |  | 0 | 0 |
Deductions |  |  |  | 0 |  | 1 | 2 |
Balance at End of Period |  |  | 1 | 1 |  | 1 | 1 |
Delmarva Power & Light Company [Member] | Allowance for Uncollectible Accounts [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 17 |  | 16 |  | 24 | 17 |
Charged to Costs and Expenses |  |  |  | 6 |  | 3 | 23 |
Charged to Other Accounts | [17] |  |  | 2 |  | 2 | 2 |
Deductions | [18] |  |  | 11 |  | 13 | 18 |
Balance at End of Period |  |  | 24 | 13 |  | 16 | 24 |
Delmarva Power & Light Company [Member] | Reserve for Obsolete Materials [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 0 |  | 0 |  | 0 | 0 |
Charged to Costs and Expenses |  |  |  | 0 |  | 1 | 1 |
Charged to Other Accounts |  |  |  | 0 |  | 0 | 0 |
Deductions |  |  |  | 0 |  | 1 | 1 |
Balance at End of Period |  |  | 0 | 0 |  | 0 | 0 |
Atlantic City Electric Company [Member] | Allowance for Uncollectible Accounts [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | 17 |  | 18 |  | 27 | 17 |
Charged to Costs and Expenses |  |  |  | 11 |  | 8 | 32 |
Charged to Other Accounts | [19] |  |  | 2 |  | 2 | 2 |
Deductions | [20] |  |  | 12 |  | 19 | 24 |
Balance at End of Period |  |  | 27 | 19 |  | 18 | 27 |
Atlantic City Electric Company [Member] | Reserve for Obsolete Materials [Member] |  |  |  |  |  |  |  |
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |  |  |  |  |  |
Balance at Beginning of Period |  | $ 0 |  | 1 |  | 1 | 0 |
Charged to Costs and Expenses |  |  |  | 0 |  | 0 | 1 |
Charged to Other Accounts |  |  |  | 0 |  | 0 | 0 |
Deductions |  |  |  | 0 |  | 0 | 0 |
Balance at End of Period |  |  | $ 1 | $ 1 |  | $ 1 | $ 1 |
[1] | Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $13 million, $15 million, and $23 million for the years ended December 31, 2018, 2017 and 2016, respectively.
[2] | Includes charges for late payments and non-service receivables
[3] | Primarily represents the addition of PHI's results as of March 23, 2016, the date of the merger
[4] | Write-off of individual accounts receivable.
[5] | Primarily reflects the reclassification of assets as held for sale.
[6] | Primarily reflects the reclassification of assets as held for sale.
[7] | Primarily charges for late payments and non-service receivables.
[8] | Write-off of individual accounts receivable.
[9] | Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $13 million, $15 million, and $23 million for the years ended December 31, 2018, 2017, and 2016, respectively.
[10] | Primarily charges for late payments.
[11] | Write-off of individual accounts receivable.
[12] | Write-off of individual accounts receivable.
[13] | Primarily charges for late payments.
[14] | Write-off of individual accounts receivable.
[15] | Primarily charges for late payments.
[16] | Write-off of individual accounts receivable.
[17] | Primarily charges for late payments.
[18] | Write-off of individual accounts receivable.
[19] | Primarily charges for late payments.
[20] | Write-off of individual accounts receivable.

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