The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 958
-SubTopic 225
-Section 45
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84241808&loc=d3e92212-112881

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2921-110230

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The period end amount owned by the reporting utility of a jointly owned utility plant in service.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033

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- Definition

Identifies the name or location used by the utility of a jointly owned utility plant.

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- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

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The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

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The proportionate share of interest (percent) in a jointly owned utility plant.

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Jointly-Owned Electric Plants (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Proportionate ownership interest In jointly-owned facilities [Abstract]
Impairment charges	$ 446	$ 7	$ 2
FPL[Member] \| Jointly Owned Nuclear Power Plant 1 [Member]
Proportionate ownership interest In jointly-owned facilities [Abstract]
Facility Name	St. Lucie Unit No. 2
Proportionate ownership share	85.00%
Gross Investment	$ 2,205
Accumulated Depreciation	863
Construction Work in Progress	$ 36
FPL[Member] \| Jointly Owned Nuclear Power Plant 2 [Member]
Proportionate ownership interest In jointly-owned facilities [Abstract]
Facility Name	St. Johns River Power Park units and coal terminal
Proportionate ownership share	20.00%
Gross Investment	$ 394
Accumulated Depreciation	215
Construction Work in Progress	$ 0
FPL[Member] \| Jointly Owned Nuclear Power Plant 3 [Member]
Proportionate ownership interest In jointly-owned facilities [Abstract]
Facility Name	Scherer Unit No. 4
Proportionate ownership share	76.00%
Gross Investment	$ 1,146
Accumulated Depreciation	419
Construction Work in Progress	24
NEER [Member]
Proportionate ownership interest In jointly-owned facilities [Abstract]
Impairment charges	$ 420
NEER [Member] \| Jointly Owned Electricity Generation Plant 1 [Member]
Proportionate ownership interest In jointly-owned facilities [Abstract]
Facility Name	Duane Arnold
Proportionate ownership share	70.00%
Gross Investment	$ 61
Accumulated Depreciation	0
Construction Work in Progress	$ 4
NEER [Member] \| Jointly Owned Electricity Generation Plant 2 [Member]
Proportionate ownership interest In jointly-owned facilities [Abstract]
Facility Name	Seabrook
Proportionate ownership share	88.23%
Gross Investment	$ 1,181
Accumulated Depreciation	302
Construction Work in Progress	$ 78
NEER [Member] \| Jointly Owned Electricity Generation Plant 3 [Member]
Proportionate ownership interest In jointly-owned facilities [Abstract]
Facility Name	Wyman Station Unit No. 4
Proportionate ownership share	87.49%
Gross Investment	$ 26
Accumulated Depreciation	4
Construction Work in Progress	$ 0
Corporate and Other [Member] \| Jointly Owned Electricity Transmission and Distribution System [Member]
Proportionate ownership interest In jointly-owned facilities [Abstract]
Facility Name	Transmission substation assets located in Seabrook, New Hampshire
Proportionate ownership share	88.23%
Gross Investment	$ 78
Accumulated Depreciation	14
Construction Work in Progress	$ 3