Financial Assets And Financial Liabilities (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Financial Assets And Financial Liabilities [Abstract]
Transfers of financial instruments sold, but not yet purchased from level 3 to level 1		$ 1
Transfers of financial instruments sold, but not yet purchased from level 1 to level 3	$ 1
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes	$ 7,000		$ 600

The carrying value of funds, segregated for regulatory purposes and for the exclusive benefit of customers, outstanding loaned in the form of security resale agreements if the agreement requires the purchaser to resell the identical security purchased or a security that meets the definition of "substantially the same" in the case of a dollar roll. Also includes purchases of participations in pools of securities that are subject to a resale agreement.

No definition available.

Name:	ibkr_SegregatedSecuritiesPurchasedUnderAgreementsToResell
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant