Business Segment Information - Summarized Financial Information Concerning Segments (Additional Information) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information
Full cost ceiling limitation impairment	$ 1,100.0	$ 164.8
Exploration and Production
Segment Reporting Information
Full cost ceiling limitation impairment	$ 1,100.0	$ 164.8

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 FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 360

-Section S99

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27015634&loc=d3e516453-122869

Reference 2: 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

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