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Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Mar. 23, 2016 | Sep. 30, 2017 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | $ 20,000,000 |  |  |  | $ 2,000,000
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 489,000,000 |  | $ 468,000,000 |  | 446,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 20,000,000 |  |  |  | 2,000,000
Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  | $ 203,000,000 | $ 84,000,000 |  | $ 138,000,000 |  | 0 |  |  |  | 0
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 489,000,000 |  | 468,000,000 |  | 446,000,000
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  | 180,000,000 |  |  |  |  |  | 34,000,000
Asset Retirement Obligation, Revision of Estimate |  | 203,000,000 | 84,000,000 |  | 138,000,000 |  | 0 |  |  |  | 0
PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 0 |  |  |  | 0
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 0 |  | 0 |  | 0
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 0 |  |  |  | 0
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 0 |  |  |  | 0
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 0 |  | 0 |  | 0
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 0 |  |  |  | 0
Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 0 |  | 0 |  |
Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  | $ 2,000,000 | 20,000,000 |  |  |  |
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  | 0 |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  | 2,000,000 | 20,000,000 |  |  |  |
Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  | $ 0 |  |  |  |  |  |  |
Asset Retirement Obligation, Accretion Expense | [1] |  |  | 0 |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  | 0 |  |  |  |  |  |  |
Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 22,000,000 |  |  |  | 0
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 0 |  | 0 |  | 0
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 22,000,000 |  |  |  | 0
Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | (1,000,000) |  |  |  | 1,000,000
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 0 |  | 0 |  | 0
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | (1,000,000) |  |  |  | 1,000,000
Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | (1,000,000) |  |  |  | 2,000,000
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 0 |  | 0 |  | 0
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | (1,000,000) |  |  |  | 2,000,000
Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 0 |  |  |  | 0
Asset Retirement Obligation, Accretion Expense | [1] |  |  |  |  |  | 0 |  | 0 |  | 0
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 0 |  |  |  | 0
Nonnuclear Decommissioning Asset Retirement Obligation [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | (3,000,000) |  |  |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 199,000,000 |  | 197,000,000 |  | 199,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 35,000,000 |  | (1,000,000) |  |
Development projects | [2] |  |  |  |  |  |  |  | 1,000,000 |  |
Asset Retirement Obligation, Accretion Expense |  |  |  |  |  |  | 10,000,000 |  | 10,000,000 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | (3,000,000) |  | (7,000,000) |  |
Payments |  |  |  |  |  |  | (1,000,000) |  | (5,000,000) |  |
ARO ending balance |  | 238,000,000 |  |  |  | 199,000,000 | 238,000,000 |  | 197,000,000 |  | 199,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 35,000,000 |  | (1,000,000) |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 28,000,000 |  | 27,000,000 |  | 28,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 0 |  | (1,000,000) |  |
Development projects | [2] |  |  |  |  |  |  |  | 0 |  |
Asset Retirement Obligation, Accretion Expense | [3] |  |  |  |  |  | 1,000,000 |  | 1,000,000 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | 0 |  | 0 |  |
Payments |  |  |  |  |  |  | 0 |  | (1,000,000) |  |
ARO ending balance |  | 28,000,000 |  |  |  | 28,000,000 | 28,000,000 |  | 27,000,000 |  | 28,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 0 |  | (1,000,000) |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 24,000,000 |  | 24,000,000 |  | 24,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 2,000,000 |  | 2,000,000 |  |
Development projects | [2] |  |  |  |  |  |  |  | 0 |  |
Asset Retirement Obligation, Accretion Expense | [3] |  |  |  |  |  | 1,000,000 |  | 0 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | 0 |  | 0 |  |
Payments |  |  |  |  |  |  | (2,000,000) |  | (2,000,000) |  |
ARO ending balance |  | 25,000,000 |  |  |  | 24,000,000 | 25,000,000 |  | 24,000,000 |  | 24,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 2,000,000 |  | 2,000,000 |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 14,000,000 |  | 16,000,000 |  | 14,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 36,000,000 |  | 2,000,000 |  |
Development projects | [2] |  |  | $ 0 |  |  |  |  |  |  |
Asset Retirement Obligation, Accretion Expense |  |  |  |  |  |  | 0 |  | 0 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  |  |  | 0 |  |
Payments |  |  |  |  |  |  | 0 |  | 0 |  |
ARO ending balance |  | 52,000,000 |  |  |  | 14,000,000 | 52,000,000 |  | 16,000,000 |  | 14,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 36,000,000 |  | 2,000,000 |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | 0 |  |  |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 2,000,000 |  | 3,000,000 |  | 2,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  | 22,000,000 |  |  |  | 34,000,000 |  | 1,000,000 |  |
Development projects | [2] |  |  |  |  |  |  |  | 0 |  |
Asset Retirement Obligation, Accretion Expense |  |  |  |  |  |  | 0 |  | 0 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | 0 |  | 0 |  |
Payments |  |  |  |  |  |  | 0 |  | 0 |  |
ARO ending balance |  | 37,000,000 |  |  |  | 2,000,000 | 37,000,000 |  | 3,000,000 |  | 2,000,000
Asset Retirement Obligation, Revision of Estimate |  |  | 22,000,000 |  |  |  | 34,000,000 |  | 1,000,000 |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 9,000,000 |  | 10,000,000 |  | 9,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 1,000,000 |  | 1,000,000 |  |
Development projects | [2] |  |  |  |  |  |  |  | 0 |  |
Asset Retirement Obligation, Accretion Expense |  |  |  |  |  |  | 0 |  | 0 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | 0 |  | 0 |  |
Payments |  |  |  |  |  |  | 0 |  | 0 |  |
ARO ending balance |  | 11,000,000 |  |  |  | 9,000,000 | 11,000,000 |  | 10,000,000 |  | 9,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 1,000,000 |  | 1,000,000 |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 3,000,000 |  | 3,000,000 |  | 3,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 1,000,000 |  | 0 |  |
Development projects | [2] |  |  |  |  |  |  |  | 0 |  |
Asset Retirement Obligation, Accretion Expense |  |  |  |  |  |  | 0 |  | 0 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | 0 |  | 0 |  |
Payments |  |  |  |  |  |  | 0 |  | 0 |  |
ARO ending balance |  | 4,000,000 |  |  |  | 3,000,000 | 4,000,000 |  | 3,000,000 |  | 3,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 1,000,000 |  | 0 |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Enterprise [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  |  |  | (7,000,000) |  |
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 121,000,000 |  | 113,000,000 |  | 121,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 7,000,000 |  | (13,000,000) |  |
Development projects | [2] |  |  |  |  |  |  |  | 0 |  |
Asset Retirement Obligation, Accretion Expense | [3] |  |  |  |  |  | 4,000,000 |  | 7,000,000 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | 0 |  | 0 |  |
Payments |  |  |  |  |  |  | (3,000,000) |  | (2,000,000) |  |
ARO ending balance |  | 121,000,000 |  |  |  | 121,000,000 | 121,000,000 |  | 113,000,000 |  | 121,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 7,000,000 |  | (13,000,000) |  |
Nuclear decommissioning | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | 8,734,000,000 |  | 9,662,000,000 | [4] | 8,734,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  | 772,000,000 |  |  |  |  |  | 444,000,000 |  |
Development projects |  |  |  |  |  |  | (58,000,000) |  | 8,000,000 |  |
Asset Retirement Obligation, Accretion Expense |  |  |  |  |  |  | 478,000,000 |  | 458,000,000 |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  |  | (77,000,000) |  | 34,000,000 |  |
ARO ending balance |  | 10,005,000,000 |  |  |  | 8,734,000,000 | 10,005,000,000 |  | 9,662,000,000 | [4] | 8,734,000,000
Asset Retirement Obligation, Revision of Estimate |  |  | $ 772,000,000 |  |  |  |  |  | 444,000,000 |  |
Asset Retirement Obligation, Current |  | 22,000,000 |  |  |  |  | 22,000,000 |  | 13,000,000 |  |
Nuclear decommissioning | Exelon Enterprise [Member] |  |  |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
ARO beginning balance |  |  |  |  | $ 393,000,000 |  | 384,000,000 |  | 393,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | 80,000,000 |  | (11,000,000) |  |
Development projects | [2] |  |  |  |  |  |  |  | 1,000,000 |  |
Asset Retirement Obligation, Accretion Expense |  |  |  |  |  |  | 16,000,000 |  | 18,000,000 |  |
Payments |  |  |  |  |  |  | (6,000,000) |  | (10,000,000) |  |
ARO ending balance |  | $ 471,000,000 |  |  |  | $ 393,000,000 | 471,000,000 |  | 384,000,000 |  | $ 393,000,000
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  |  | $ 80,000,000 |  | $ (11,000,000) |  |
[1] | Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2] | .
[3] | (b)In 2018, Pepco recorded an increase of $22 million in Operating and maintenance expense primarily related to asbestos identified at its Buzzard Point property as part of an annual ARO study. Buzzard Point is a waterfront property in the District of Columbia occupied by an active substation and former Pepco operated steam plant building, which Pepco retired and closed in 1981.
[4] | Includes $22 million and $13 million as the current portion of the ARO at December 31, 2018 and 2017, respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets.

X
- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848 + Details
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- Definition Amount of cash paid during the period to settle an asset retirement obligation. Amounts paid to settle an asset retirement obligation are generally included in the operating section of the Statement of Cash Flows. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 17 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3367-108585 + Details
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- Definition Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of asset retirement obligations incurred during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of increase (decrease) in asset retirement obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 35 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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