Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended					1 Months Ended		12 Months Ended	3 Months Ended				1 Months Ended	3 Months Ended
	Jun. 30, 2010	Jul. 31, 2011	Dec. 31, 2011 Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Fair Value, Inputs, Level 3 [Member] Commodity [Member]	Jun. 30, 2010 Fair Value, Measurements, Nonrecurring [Member] State Line [Member]	Mar. 31, 2011 Fair Value, Measurements, Nonrecurring [Member] State Line [Member] Other Operating Expense [Member]	Jun. 30, 2010 Fair Value, Measurements, Nonrecurring [Member] State Line [Member] Other Operating Expense [Member]	Dec. 31, 2010 Fair Value, Measurements, Nonrecurring [Member] Salem Harbor [Member] Other Operating Expense [Member]	Sep. 30, 2011 Fair Value, Measurements, Nonrecurring [Member] Emissions Allowances [Member] Other Operating Expense [Member]	Mar. 31, 2011 Maximum [Member] Fair Value, Measurements, Nonrecurring [Member] State Line [Member]	Dec. 31, 2010 Maximum [Member] Fair Value, Measurements, Nonrecurring [Member] Salem Harbor [Member]	Sep. 30, 2011 Maximum [Member] Fair Value, Measurements, Nonrecurring [Member] Emissions Allowances [Member]	Sep. 30, 2010 Virginia Power [Member] Fair Value, Measurements, Nonrecurring [Member] Emissions Allowances [Member] Other Operating Expense [Member]	Sep. 30, 2011 Virginia Power [Member] Fair Value, Measurements, Nonrecurring [Member] Emissions Allowances [Member] Other Operating Expense [Member]	Sep. 30, 2010 Virginia Power [Member] Maximum [Member] Fair Value, Measurements, Nonrecurring [Member] Emissions Allowances [Member]
Commodity derivatives categorized as Level 3 fair value measurements, net liability				$ 71
Commodity derivatives categorized as Level 3 fair value measurements, hypothetical 10% increase in commodity prices, increase to net liability			73
Commodity derivatives categorized as Level 3 fair value measurements, hypothetical 10% decrease in commodity prices, decrease to net liability			74
Impairment charge						55	163	31
Impairment charge after tax	95					39	107	20					8
Estimated fair value					59					1	1
So2 Emissions Allowances Obtained For Arp And Cair Compliance		57							57					43
Impairment Of Intangible Assets After Tax									34					26
Salem Harbor, impairment charge									57				13	43
Maximum Fair Value Of So2 Emissions Allowances												$ 1			$ 1