Amount of income (loss) for proportionate share of equity method investee's income (loss).

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

Investments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Investments - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Options Clearing Corporation
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	40.00%		40.00%
Equity earnings in other income	$ 49	$ 15	$ 84	$ 51
Options Clearing Corporation \| Restatement Adjustment
Schedule of Equity Method Investments [Line Items]
Equity earnings in other income	$ 36		$ 36	$ 19
BIDS Trading, LP
Schedule of Equity Method Investments [Line Items]
Investment ownership percentage	9.00%		9.00%