Commitments and Contingencies - Additional Information (Detail)	1 Months Ended	12 Months Ended
	May 31, 2010 USD ($)	Dec. 31, 2012 USD ($) Contract	Dec. 31, 2012 AUD	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	May 29, 2009 AUD	Dec. 31, 2012 Alcoa [Member] USD ($) Contract	Dec. 31, 2012 Oswal [Member] USD ($)	Aug. 31, 2011 Phoenix [Member] acre	Jan. 31, 2012 Burrup Holdings Limited (Yara Pilbara Holdings Pty Limited ) [Member]	Jan. 31, 2012 Yara International [Member]
Contingencies And Commitments [Line Items]
Accrued liability for legal contingencies		$ 12,000,000
Damages sought by plaintiffs		100,000,000
Cost for the restoration of plaintiffs' property	87,000,000	61,000,000
Percentage of general partner interest acquired									75.00%
Percentage of limited partner interest acquired									75.00%
Area of Land									3,000
Maximum Expected contractual general damages under long term contracts							158,000,000	491,000,000
Number of Contract							2
Maximum expected contractual liquidated damages under long term contracts		5,700,000	200,000,000
Long term contracts unenforceable as penalty		2	2
Approximate percentage of natural gas volumes sold under long-term contracts that have liquidated damages provisions		90.00%	90.00%
Range of estimates for macroeconomic impact			300,000,000
Range of estimates for macroeconomic impact			2,500,000,000
Compensation related gas shortage			20,000,000
Pure economic losses			1,300,000,000
Property damage settlement amount			32,500,000
Maximum fine associated with the alleged offense						50,000
Validity of pipeline license		21 years	21 years
Percentage of combined ownership held by the plaintiff in the company		65.00%	65.00%
Percentage of acquisition										49.00%	51.00%
Maximum cost considered to be recognized for additional reserve		300,000
Undiscounted reserve for environmental remediation		104,000,000
Net rental expenses		$ 76,000,000		$ 64,000,000	$ 46,000,000
Lease Expiration		2035	2035