Fair Value Measurements (Narrative) (Details) (USD $) In Millions	6 Months Ended
	Jun. 30, 2011
Long-lived assets estimated fair value	$ 59
State line evaluation, impairment charge	163
State line evaluation, impairment charge after tax	95
State line evaluation, estimated fair value	1
Other Operating Expense [Member]
State line evaluation, impairment charge	55
State line evaluation, impairment charge after tax	39
Level 3 [Member]
Commodity derivatives categorized as Level 3 fair value measurements, hypothetical 10% increase in commodity prices, decrease to net asset	(112)
Commodity derivatives categorized as Level 3 fair value measurements, hypothetical 10% decrease in commodity prices, increase to net asset	113
Level 3 [Member] | Commodity Transactions [Member]
Commodity derivatives categorized as Level 3 fair value measurements, net asset	$ 122