Segment Information (Financial Data - Operating Revenues including inter segment revenues) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ 2,984	$ 3,930
Operating Segments | Electric
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,203	1,412
Operating Segments | Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	647	804
Operating Segments | Gas Storage and Pipelines
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	57	52
Operating Segments | Power and Industrial Projects
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	567	575
Operating Segments | Energy Trading
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	711	1,314
Operating Segments | Corporate and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	0	0
Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(201)	(227)
Reconciliation and Eliminations | Electric
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(9)	(7)
Reconciliation and Eliminations | Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(1)	(2)
Reconciliation and Eliminations | Gas Storage and Pipelines
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(1)	(1)
Reconciliation and Eliminations | Power and Industrial Projects
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(180)	(206)
Reconciliation and Eliminations | Energy Trading
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(9)	(9)
Reconciliation and Eliminations | Corporate and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ (1)	$ (2)