Acquisitions and Exit Activities (Restructuring and Related Costs) (Details) - Facility Closing - USD ($) $ in Millions		12 Months Ended
Dec. 17, 2015	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Total exit activity charges	$ 111	$ 111
Fuel, purchased power, and gas — non-utility
Restructuring Cost and Reserve [Line Items]
Total exit activity charges		5
Operation and maintenance
Restructuring Cost and Reserve [Line Items]
Total exit activity charges		10
Asset (gains) losses and impairments, net
Restructuring Cost and Reserve [Line Items]
Total exit activity charges		$ 96

Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan and expenses resulting from the write-down of assets. Excludes expenses related to a business combination, a discontinued operation or an asset retirement obligation.

Reference 1: 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

Name:	us-gaap_RestructuringCostsAndAssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration