Organization, Principles Of Consolidation And Basis Of Presentation (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Organization, Principles Of Consolidation And Basis Of Presentation [Abstract]
Total investment in low-income housing tax credit investments	$ 177.1	$ 128.0

This item represents the carrying amount of the Company's Interests in low-income housing tax credit investments accounted for under the equity method of accounting.

No definition available.

Name:	sfg_LowIncomeHousingTaxCreditInvestments
Namespace Prefix:	sfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant