Resource Management and Other Commercial Events (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended
Jan. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Mar. 31, 2013
Other Commercial Events [Line Items]
Cash proceeds from sale of nonstrategic exploration tenement asset	$ 62.6		$ 99.8	$ 53.0
Contracts revenue		$ 33.5

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

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