The dollar value of commission paid for assuming a block of business from another company.

No definition available.

Name:	sfg_ReinsuranceCedingCommissionPaid
Namespace Prefix:	sfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The dollar value of commission received for ceding a block of business to another company.

+ References

No definition available.

+ Details

Name:	sfg_ReinsuranceCedingCommissionReceived
Namespace Prefix:	sfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Value of assumed assets and corresponding statutory liabilities transferred from ceding company due to reinsurance agreement.

+ References

No definition available.

+ Details

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

- Definition

Value of ceded assets and corresponding statutory liabilities transferred to assuming company due to reinsurance agreement.

+ References

No definition available.

+ Details

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

- Definition

The number of contracts assumed through a reinsurance agreement.

+ References

No definition available.

+ Details

Name:	sfg_ReinsuranceNumberOfGroupInsuranceContractsAssumed
Namespace Prefix:	sfg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of insured individuals assumed through a reinsurance agreement.

+ References

No definition available.

+ Details

Name:	sfg_ReinsuranceNumberOfInsuredIndividualsAssumed
Namespace Prefix:	sfg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_CededCreditRiskLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of funds held as security for payments to be received under reinsurance contracts.

+ References

+ Details

Name:	us-gaap_FundsHeldUnderReinsuranceAgreementsLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The remaining unamortized carrying amount as of the balance sheet date of expected future earnings from insurance contracts acquired (also known as present value of future profits).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.10)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 20

-Section S99

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27015749&loc=d3e569990-122904

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 10

-Article 7

+ Details

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

- Details

Name:	us-gaap_ReinsurancePolicyTypeAxis=sfg_MinnesotaLifeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ReinsurancePolicyTypeAxis=sfg_ProtectiveLifeInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ReinsurancePolicyTypeAxis=sfg_TiaaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Reinsurance Of Blocks Of Business (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 NumberOfGroupInsuranceContracts NumberOfInsuredIndividuals	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Ceded Credit Risk [Line Items]
VOBA recorded	$ 17.8us-gaap_ValueOfBusinessAcquiredVOBA	$ 20.1us-gaap_ValueOfBusinessAcquiredVOBA	$ 23.4us-gaap_ValueOfBusinessAcquiredVOBA	$ 26.4us-gaap_ValueOfBusinessAcquiredVOBA
TIAA [Member]
Ceded Credit Risk [Line Items]
Ceding commission paid	75.0
Market value of assets and statutory liabilities received	705.0
Market value of trust fund assets for reinsurance contract	190.1
Number of group insurance contracts assumed	1,800
Number of insured individuals assumed	650,000
VOBA recorded	60.0
Minnesota Life [Member]
Ceded Credit Risk [Line Items]
Ceding commission paid	55.0
Market value of assets and statutory liabilities received	500.0
Market value of trust fund assets for reinsurance contract	562.3
Protective Life Insurance Company [Member]
Ceded Credit Risk [Line Items]
Ceding commission received	90.0
Market value of assets and statutory liabilities transferred	$ 790.0