Document And Entity Information (USD $)	9 Months Ended
	Sep. 30, 2011	Oct. 25, 2011	Jun. 30, 2011
Entity Registrant Name	Nicor Inc.
Entity Central Index Key	0000072020
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 2,500,000,000
Entity Common Stock, Shares Outstanding		45,545,154
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2011