Commitment And Contingencies [Line Items]

No definition available.

Name:	ibkr_CommitmentAndContingenciesLineItems
Namespace Prefix:	ibkr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum Aggregate Loss, If Securities' Price Falls To Zero And No Debts Collected

+ References

No definition available.

+ Details

Name:	ibkr_MaximumAggregateLossIfSecuritiesPriceFallsToZeroAndNoDebtsCollected
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

+ References

No definition available.

+ Details

Name:	us-gaap_MarketableSecuritiesGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 3)
-URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717

+ Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments, Contingencies and Guarantees (Narrative) (Details) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Feb. 27, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitment And Contingencies [Line Items]
Rent expense		$ 15	$ 15	$ 16
Total future minimum annual lease commitments		$ 167
Subsequent Event [Member]
Commitment And Contingencies [Line Items]
Aggregate loss on securities	$ 47
Maximum aggregate loss, if securities' price falls to zero and no debts collected	$ 59