Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 16, 2018	Jun. 30, 2017
Entity Registrant Name	FEDERATED INVESTORS INC /PA/
Entity Central Index Key	0001056288
Trading Symbol	FII
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2017
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Amendment Flag	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2,600,000,000
Subsequent Event [Member] | Class A [Member]
Entity Common Stock, Shares Outstanding		9,000
Subsequent Event [Member] | Class B [Member]
Entity Common Stock, Shares Outstanding		100,984,808