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Retirement Benefits (Assumed Health Care Cost Trend Rates For Next Year) (Details)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Assumed Health Care Cost Trend Rates For Next Year [Line Items]    
Rate to which the cost trend is assumed to decline (the ultimate trend rate) 4.50%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate [1] 4.50%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate [1]
Medical [Member]    
Assumed Health Care Cost Trend Rates For Next Year [Line Items]    
Assumed health care cost trend rates for next year 6.90%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ sfg_AssumedHealthCareCostTrendRatesForNextYearAxis
= sfg_MedicalMember		 7.10%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ sfg_AssumedHealthCareCostTrendRatesForNextYearAxis
= sfg_MedicalMember
Prescriptions [Member]    
Assumed Health Care Cost Trend Rates For Next Year [Line Items]    
Assumed health care cost trend rates for next year 7.20%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ sfg_AssumedHealthCareCostTrendRatesForNextYearAxis
= sfg_PrescriptionsMember		 7.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ sfg_AssumedHealthCareCostTrendRatesForNextYearAxis
= sfg_PrescriptionsMember
Health Maintenance Organization [Member]    
Assumed Health Care Cost Trend Rates For Next Year [Line Items]    
Assumed health care cost trend rates for next year 5.70%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ sfg_AssumedHealthCareCostTrendRatesForNextYearAxis
= sfg_HealthMaintenanceOrganizationMember		 6.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ sfg_AssumedHealthCareCostTrendRatesForNextYearAxis
= sfg_HealthMaintenanceOrganizationMember
[1]

*Year that the rate reaches the ultimate trend is 2027.

Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plans. A one-percentage-point change in assumed health care cost trend rates would have the following effects: