Commitments, Guarantees and Contingencies - Other Legal Proceedings (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Nuclear plant decommissioning trusts	$ 2,678,000,000	$ 2,514,000,000
Parental support agreement	3,800,000,000
Nuclear Plant Matters
Loss Contingencies [Line Items]
Nuclear plant decommissioning trusts	2,700,000,000
FES
Loss Contingencies [Line Items]
Nuclear plant decommissioning trusts	1,856,000,000	1,552,000,000
FES | Nuclear Plant Matters
Loss Contingencies [Line Items]
Nuclear plant decommissioning trusts	1,900,000,000
NG | Parent Support Agreement | FES | Nuclear Plant Matters
Loss Contingencies [Line Items]
Parental support agreement	400,000,000
Revolving Credit Facility | Line of Credit
Loss Contingencies [Line Items]
Maximum amount borrowed under revolving credit facility	5,000,000,000	500,000,000
Revolving Credit Facility | Line of Credit | Nuclear Plant Matters
Loss Contingencies [Line Items]
Maximum amount borrowed under revolving credit facility	$ 500,000,000
Revolving Credit Facility | Line of Credit | FES
Loss Contingencies [Line Items]
Maximum amount borrowed under revolving credit facility		$ 500,000,000