Acquisitions and Dispositions (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2010
Summary of the allocation of the purchase price to the assets and liabilities acquired in a business combination
Property, plant and equipment	$ 2,590
Goodwill	907
Current assets	178
Total assets acquired	3,675
Current liabilities	(167)
Deferred tax liabilities	(907)
Asset retirement obligations	(242)
Net assets acquired	2,359
Exchange [Member]
Summary of the allocation of the purchase price to the assets and liabilities acquired in a business combination
Property, plant and equipment	2,020
Goodwill	688
Current assets	155
Total assets acquired	2,863
Current liabilities	(135)
Deferred tax liabilities	(688)
Asset retirement obligations	(188)
Net assets acquired	1,852
Acquisition [Member]
Summary of the allocation of the purchase price to the assets and liabilities acquired in a business combination
Property, plant and equipment	570
Goodwill	219
Current assets	23
Total assets acquired	812
Current liabilities	(32)
Deferred tax liabilities	(219)
Asset retirement obligations	(54)
Net assets acquired	$ 507