Commitments and Contingencies (Insurance) (Details) $ in Millions	Sep. 30, 2017 USD ($)
Insurance [Abstract]
Maximum obtainable amount of private liability insurance available under Price-Anderson Act	$ 450
Amount of secondary financial protection liability insurance coverage per incident	13,000
Potential Retrospective Assessments Under Secondary Financial Protection System	1,000
Potential Retrospective Assessments Under Secondary Financial Protection System Payable Per Incident Per Year	152
Amount of coverage per occurrence per site for property damage, decontamination and premature decommissioning risks	2,750
Amount of sublimit for nonnuclear perils per occurrence per site under nuclear insurance mutual companies for property damage decontamination and premature decommissioning risks	1,500
Potential amount of retrospective assessment per occurrence per site for property damage, decontamination and premature decommissioning risks	178
FPL [Member]
Insurance [Abstract]
Potential Retrospective Assessments Under Secondary Financial Protection System	509
Potential Retrospective Assessments Under Secondary Financial Protection System Payable Per Incident Per Year	76
Potential amount of retrospective assessment per occurrence per site for property damage, decontamination and premature decommissioning risks	108
Seabrook Station [Member]
Insurance [Abstract]
Potential retrospective assessment recoverable from minority interest for nuclear liability secondary financial protection	15
Potential retrospective assessment recoverable from minority interest for property damage, decontamination and premature decommissioning risks	2
Duane Arnold Energy Center [Member]
Insurance [Abstract]
Potential retrospective assessment recoverable from minority interest for nuclear liability secondary financial protection	38
Amount of sublimit for nonnuclear perils per occurrence per site under nuclear insurance mutual companies for property damage decontamination and premature decommissioning risks	1,000
Potential retrospective assessment recoverable from minority interest for property damage, decontamination and premature decommissioning risks	5
St Lucie Unit No. 2 [Member]
Insurance [Abstract]
Potential retrospective assessment recoverable from minority interest for nuclear liability secondary financial protection	19
Potential retrospective assessment recoverable from minority interest for property damage, decontamination and premature decommissioning risks	$ 4