Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Mar. 31, 2013	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2013 Argentina [Member]	Jun. 30, 2012 Canada [Member]
Summary of Significant Accounting Policies [Line Items]
Discount rate				10.00%
Write-down of the carrying value of Oil and Gas properties	$ 65.0	$ 641.0	$ 521.0		$ 65.0	$ 1,200.0
Write-down of the carrying value of Oil and Gas properties, net of tax					$ 42	$ 870

The excess of unamortized costs capitalized within a cost center, less related deferred income taxes, over the cost center ceiling limitation, which is charged to expense for oil and gas producing companies that use full cost method of accounting for investments in oil and gas producing properties.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 10

-Paragraph c

-Subparagraph 4(ii)

-Article 4

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration