Asset Retirement Obligations - Unrealized Gain on NDT Funds (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments		$ 13,272	$ 11,061
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments		13,272	11,061
Unrealized Gain (Loss) on Investments		(10)	(1)	$ 7
Collateral Pledged [Member] | Unregulated Operation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Unrealized Gain (Loss) on Investments	[1],[2]	521	194	(197)
Collateral Pledged [Member] | Regulated Operation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Unrealized Gain (Loss) on Investments	[3]	455	$ 216	$ (282)
Assets, Total [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments		$ 13,349

[1] Excludes $(10) million, $(1) million and $7 million of net unrealized gains (losses) related to the Zion Station pledged assets in 2017, 2016 and 2015, respectively. Net unrealized gains related to Zion Station pledged assets are included in the Other current liabilities and Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets

[2] Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.

[3] Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets.