Segment Information (Financial Data - Operating Revenues including inter segment revenues) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ 3,930	$ 2,516
Operating Segments [Member] | Electric [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,412	1,219
Operating Segments [Member] | Gas [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	804	604
Operating Segments [Member] | Gas Storage and Pipelines [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	52	27
Operating Segments [Member] | Power and Industrial Projects [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	575	490
Operating Segments [Member] | Energy Trading [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,314	393
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	0	0
Intersegment Eliminations [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(227)	(217)
Intersegment Eliminations [Member] | Electric [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(7)	(6)
Intersegment Eliminations [Member] | Gas [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(2)	(1)
Intersegment Eliminations [Member] | Gas Storage and Pipelines [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(1)	(2)
Intersegment Eliminations [Member] | Power and Industrial Projects [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(206)	(205)
Intersegment Eliminations [Member] | Energy Trading [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	(9)	(11)
Intersegment Eliminations [Member] | Corporate and Other [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Inter-segment Revenues	$ (2)	$ 8