Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Feb. 02, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	PRINCIPAL FINANCIAL GROUP INC
Entity Central Index Key	0001126328
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 18.5
Entity Common Stock, Shares Outstanding		289,656,803
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY