Segment Information (Financial Data - Operating Revenues including inter segment revenues) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ 2,595	$ 2,387	$ 9,223	$ 7,128
Operating Segments [Member] | Electric [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,358	1,458	4,049	3,942
Operating Segments [Member] | Gas [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	149	161	1,182	1,013
Operating Segments [Member] | Gas Storage and Pipelines [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	49	34	146	92
Operating Segments [Member] | Power and Industrial Projects [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	605	512	1,703	1,431
Operating Segments [Member] | Energy Trading [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	664	463	2,797	1,307
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	0	1	1	2
Intersegment Eliminations [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(230)	(242)	(655)	(659)
Intersegment Eliminations [Member] | Electric [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(8)	(6)	(22)	(19)
Intersegment Eliminations [Member] | Gas [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(1)	(2)	(5)	(4)
Intersegment Eliminations [Member] | Gas Storage and Pipelines [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(1)	2	(9)	(2)
Intersegment Eliminations [Member] | Power and Industrial Projects [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(211)	(231)	(593)	(621)
Intersegment Eliminations [Member] | Energy Trading [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(8)	(13)	(24)	(36)
Intersegment Eliminations [Member] | Corporate and Other [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ (1)	$ 8	$ (2)	$ 23