v3.7.0.1

Acquisition (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jan. 17, 2017 USD ($)	Feb. 05, 2016 USD ($) MW
North American Power [Member]
Business Acquisition [Line Items]
Ownership percentage of acquiree			100.00%
Business combination, recognized identifiable assets acquired and liabilities assumed, net			$ 105
Granite Ridge Energy Center [Member]
Business Acquisition [Line Items]
Business combination, recognized identifiable assets acquired and liabilities assumed, net				$ 500
Power generation capacity | MW				745
Summer Peaking Capacity | MW				695
Osprey Energy Center [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Productive Assets		$ 166
Gain (Loss) on Sale of Assets and Asset Impairment Charges	$ 27

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Power generation capacity

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Summer Peaking Capacity

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 55
-Paragraph 37
-URI http://asc.fasb.org/extlink&oid=84160947&loc=d3e2207-128464

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

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The cash inflow from the sale of property, plant and equipment (capital expenditures), software, and other intangible assets.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

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