Organization, Principles Of Consolidation And Basis Of Presentation (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Organization, Principles Of Consolidation And Basis Of Presentation [Abstract]
Total investment in tax advantaged investments	$ 279.0	$ 277.0
Carrying Value of PAM Investments	$ 262.8	$ 257.5

This item represents the carrying amount of the Company's Interests in tax advantaged 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