Note 3 - Merger with Nicor (Detail) - Additional Intangible Assets Recorded From Merger (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Trade names:
Fair Value	$ 101
Retail Operations [Member] \| Trade Names [Member]
Trade names:
Fair Value	29
Weighted average amortization period	15 years
Retail Operations [Member] \| Customer Relationships [Member]
Trade names:
Fair Value	53
Weighted average amortization period	10 years
Cargo Shipping [Member] \| Trade Names [Member]
Trade names:
Fair Value	15
Weighted average amortization period	15 years
Cargo Shipping [Member] \| Customer Relationships [Member]
Trade names:
Fair Value	$ 4
Weighted average amortization period	18 years

The aggregate amount assigned to a major class of finite-lived intangible assets acquired either individually or as part of a group of assets (in either an asset acquisition or business combination). A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16265-109275

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 44

-Subparagraph a(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant