Commitments and Contingencies - Additional Information (Detail) In Millions, unless otherwise specified	9 Months Ended		1 Months Ended
	Sep. 30, 2013 USD ($) Contract Barrels	Sep. 30, 2013 AUD Contract Barrels	Oct. 31, 2013 Subsequent Event [Member] USD ($)
Contingencies And Commitments [Line Items]
Accrued liability for legal contingencies	$ 8
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%
Maximum expected contractual liquidated damages under long term contracts		50
Maximum Previous expected contractual liquidated damages under long term contracts		200
Natural gas customer lawsuit filling date			October 31, 2013
General damages claims against the company's subsidiaries and seeks			19
Undiscounted reserve for environmental remediation	$ 94
Quantity of water spill	97,000	97,000
Estimated quantity of water spill	60,000	60,000