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	3 Months Ended
	Mar. 31, 2013
AOCI After-Tax	$ (136)
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	(49)
Commodity | Gas Energy Contract
AOCI After-Tax	(20)
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	(14)
Maximum Term	31 months
Commodity | Electricity Energy Contract
AOCI After-Tax	31
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	(12)
Maximum Term	33 months
Commodity | Other Energy Contract
AOCI After-Tax	8
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	4
Maximum Term	38 months
Interest rate
AOCI After-Tax	(155)
Amounts Expected to be Reclassified to Earnings during the next 12 Months After-Tax	$ (27)
Maximum Term	358 months