Document and Entity Information (USD $) In Billions, except Share data	6 Months Ended
	Jun. 30, 2011	Aug. 05, 2011	Jun. 30, 2010
Document and Entity Information [Abstract]
Entity Registrant Name	Symetra Financial CORP
Entity Central Index Key	0001403385
Document Type	10-Q
Document Period End Date	Jun. 30, 2011
Amendment Flag	false
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			$ 1.0
Entity Common Stock, Shares Outstanding		118,538,606