Retirement Benefits - Gross Accumulated Other Comprehensive Loss and Regulatory Assets (Liabilities) not Recognized as Components of Periodic Benefit Cost (Details) - USD ($)
$ in Millions

Dec. 31, 2016

Dec. 31, 2015

[1]

. Retirement Benefits (All Registrants) As of December 31, 2016, Exelon sponsored defined benefit pension plans and other postretirement benefit plans for essentially all employees. Effective March 23, 2016, Exelon became the sponsor of all of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets. As a result, PHI's benefit plan net obligation and related regulatory assets were transferred to Exelon and remeasured at the merger date using current assumptions, including discount rates. The table below shows the pension and other postretirement benefit plans in which employees of each operating company participated at December 31, 2016. Operating Company(e)Name of Plan: Generation ComEd PECO BGE BSC PHI Pepco DPL ACEQualified Pension Plans: Exelon Corporation Retirement Program(a) X X X X X Exelon Corporation Cash Balance Pension Plan(a) X X X X X Exelon Corporation Pension Plan for Bargaining Unit Employees(a) X X X Exelon New England Union Employees Pension Plan(a) X Exelon Employee Pension Plan for Clinton, TMI and Oyster Creek(a) X X X X Pension Plan of Constellation Energy Group, Inc.(b) X X X X X Pension Plan of Constellation Energy Nuclear Group, LLC(c) X X X Nine Mile Point Pension Plan(c) X X Constellation Mystic Power, LLC Union Employees Pension Plan Including Plan A and Plan B(b) X Pepco Holdings LLC Retirement Plan(d) X X X X XNon-Qualified Pension Plans: Exelon Corporation Supplemental Pension Benefit Plan and 2000 Excess Benefit Plan(a) X X X X Exelon Corporation Supplemental Management Retirement Plan(a) X X X X X Constellation Energy Group, Inc. Senior Executive Supplemental Plan(b) X X X Constellation Energy Group, Inc. Supplemental Pension Plan(b) X X X Constellation Energy Group, Inc. Benefits Restoration Plan(b) X X X X Constellation Energy Nuclear Plan, LLC Executive Retirement Plan(c) X X Constellation Energy Nuclear Plan, LLC Benefits Restoration Plan(c) X X Baltimore Gas & Electric Company Executive Benefit Plan(b) X X X Baltimore Gas & Electric Company Manager Benefit Plan(b) X X X X Pepco Holdings LLC 2011 Supplemental Executive Retirement Plan(d) X X X X XConectiv Supplemental Executive Retirement Plan (d) X X X XPepco Holdings LLC Combined Executive Retirement Plan (d) X X X Atlantic City Electric Director Retirement Plan (d) X X Operating Company(e)Name of Plan: Generation ComEd PECO BGE BSC PHI Pepco DPL ACEOther Postretirement Benefit Plans: PECO Energy Company Retiree Medical Plan(a) X X X X X Exelon Corporation Health Care Program(a) X X X X X Exelon Corporation Employees’ Life Insurance Plan(a) X X X X X Exelon Corporation Health Reimbursement Arrangement Plan (a) X X X X X Constellation Energy Group, Inc. Retiree Medical Plan(b) X X X X X Constellation Energy Group, Inc. Retiree Dental Plan(b) X X X Constellation Energy Group, Inc. Employee Life Insurance Plan and Family Life Insurance Plan(b) X X X X X Constellation Mystic Power, LLC Post-Employment Medical Account Savings Plan(b) X Exelon New England Union Post-Employment Medical Savings Account Plan(a) X Retiree Medical Plan of Constellation Energy Nuclear Group LLC(c) X X X Retiree Dental Plan of Constellation Energy Nuclear Group LLC(c) X X X Nine Mile Point Nuclear Station, LLC Medical Care and Prescription Drug Plan for Retired Employees(c) X X Pepco Holdings LLC Welfare Plan for Retirees(d) X X X X X______________________(a)These plans are collectively referred to as the legacy Exelon plans.(b)These plans are collectively referred to as the legacy Constellation Energy Group (CEG) Plans.(c)These plans are collectively referred to as the legacy CENG plans.(d)These plans are collectively referred to as the legacy PHI plans.(e)Employees generally remain in their legacy benefit plans when transferring betwe