Segment Information (Financial Data - Operating Revenues including inter segment revenues) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ 2,698	$ 2,225	$ 6,628	$ 4,741
Operating Segments [Member] | Electric [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,279	1,265	2,691	2,484
Operating Segments [Member] | Gas [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	229	248	1,033	852
Operating Segments [Member] | Gas Storage and Pipelines [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	45	31	97	58
Operating Segments [Member] | Power and Industrial Projects [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	523	429	1,098	919
Operating Segments [Member] | Energy Trading [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	819	451	2,133	844
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1	1	1	1
Intersegment Eliminations [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(198)	(200)	(425)	(417)
Intersegment Eliminations [Member] | Electric [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(7)	(7)	(14)	(13)
Intersegment Eliminations [Member] | Gas [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(2)	(1)	(4)	(2)
Intersegment Eliminations [Member] | Gas Storage and Pipelines [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(7)	(2)	(8)	(4)
Intersegment Eliminations [Member] | Power and Industrial Projects [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(176)	(185)	(382)	(390)
Intersegment Eliminations [Member] | Energy Trading [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(7)	(12)	(16)	(23)
Intersegment Eliminations [Member] | Corporate and Other [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	$ 1	$ 7	$ (1)	$ 15