Fair Value Measurements (Narrative) (Details) (USD $) In Millions	3 Months Ended			1 Months Ended	9 Months Ended
	Sep. 30, 2011	Jul. 31, 2011	Sep. 30, 2011 State Line [Member] Fair Value, Measurements, Nonrecurring [Member]	Jun. 30, 2010 State Line [Member] Fair Value, Measurements, Nonrecurring [Member] Other Operating Expense [Member]	Sep. 30, 2011 Fair Value, Measurements, Nonrecurring [Member] Other Operating Expense [Member]	Sep. 30, 2011 Level 3 [Member]	Sep. 30, 2011 Level 3 [Member] Commodity Transactions [Member]
Commodity derivatives categorized as Level 3 fair value measurements, net asset							$ 42
Commodity derivatives categorized as Level 3 fair value measurements, hypothetical 10% increase in commodity prices, decrease to net asset						100
Commodity derivatives categorized as Level 3 fair value measurements, hypothetical 10% decrease in commodity prices, increase to net asset						101
So2 Emissions Allowances Obtained For Arp And Cair Compliance	57	57
Impairment of Intangible Assets (Excluding Goodwill)	57
Impairment Of Intangible Assets After Tax	34
Maximum Fair Value Of So2 Emissions Allowances	1
State line evaluation, impairment charge				163	55
State line evaluation, impairment charge after tax				95	39
State line evaluation, estimated fair value			$ 59