Segment and Related Information (Financial Data - Operating Revenues including inter segment revenues) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ 2,268	$ 2,698	$ 5,252	$ 6,628
Operating Segments | Electric
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,148	1,279	2,351	2,691
Operating Segments | Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	218	229	865	1,033
Operating Segments | Gas Storage and Pipelines
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	57	45	114	97
Operating Segments | Power and Industrial Projects
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	556	523	1,123	1,098
Operating Segments | Energy Trading
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	524	819	1,235	2,133
Operating Segments | Corporate and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1	1	1	1
Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(236)	(198)	(437)	(425)
Reconciliation and Eliminations | Electric
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(9)	(7)	(18)	(14)
Reconciliation and Eliminations | Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	0	(2)	(1)	(4)
Reconciliation and Eliminations | Gas Storage and Pipelines
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(5)	(7)	(6)	(8)
Reconciliation and Eliminations | Power and Industrial Projects
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(215)	(176)	(395)	(382)
Reconciliation and Eliminations | Energy Trading
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(7)	(7)	(16)	(16)
Reconciliation and Eliminations | Corporate and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ 0	$ 1	$ (1)	$ (1)