Commitments And Contingent Liabilities (Nuclear Insurance Coverages and Assessments) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Other Commitments [Line Items]
Maximum Aggregate Assessment Per Incident	$ 401
Maximum Aggregate Annual Assessment	60
Nuclear Insurance Aggregate Limit	3,200
Total Site Coverage for Nuclear Event [Member]
Other Commitments [Line Items]
Nuclear Liability Total	13,400
Total Site Coverage for Nuclear Event [Member] | American Nuclear Insurers [Member]
Other Commitments [Line Items]
Public And Nuclear Worker Liability Primary Layer	450
Retrospective Assessments [Member]
Other Commitments [Line Items]
Replacement Power Total	$ 76