Derivatives and Hedge Accounting Activities (Selected Information Related to Gains (Losses) on Cash Flow Hedges Included in AOCI) (Details) (USD $) In Millions, unless otherwise specified			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Commodity Gas	Dec. 31, 2012 Commodity Electricity	Dec. 31, 2012 Commodity Other	Dec. 31, 2012 Interest rate
Derivative Instruments, Gain (Loss) [Line Items]
AOCI After-Tax	$ (122)	$ (54)	$ (28)	$ 68	$ 3	$ (165)
Amounts expected to be reclassified to earnings during the next 12 months after-tax	$ (26)		$ (24)	$ 17	$ 2	$ (21)
Maximum Term			27 months	36 months	41 months	361 months