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	6 Months Ended
	Jun. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
AOCI After-Tax	$ (31)
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	5
Commodity | Gas Energy Contract
Derivative Instruments, Gain (Loss) [Line Items]
AOCI After-Tax	(7)
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	(5)
Maximum Term	31 months
Commodity | Electricity Energy Contract
Derivative Instruments, Gain (Loss) [Line Items]
AOCI After-Tax	69
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	19
Maximum Term	30 months
Commodity | Other Energy Contract
Derivative Instruments, Gain (Loss) [Line Items]
AOCI After-Tax	20
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	13
Maximum Term	35 months
Interest rate
Derivative Instruments, Gain (Loss) [Line Items]
AOCI After-Tax	(113)
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	$ (22)
Maximum Term	355 months