Acquisitions and Dispositions (Tables)

12 Months Ended

Dec. 31, 2011

Acquisitions and Dispositions [Abstract]

Summary of the allocation of the purchase price to the assets and liabilities acquired in a business combination

	Exchange			Acquisition			Total
	(Millions of dollars)
Property, plant and equipment	$	2,020		$	570		$	2,590
Goodwill		688			219			907
Current assets		155			23			178
Total assets acquired		2,863			812			3,675
Current liabilities		(135	)		(32	)		(167	)
Deferred tax liabilities		(688	)		(219	)		(907	)
Asset retirement obligations		(188	)		(54	)		(242	)
Net assets acquired	$	1,852		$	507		$	2,359