Clearing Operations (Investment Policy) (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Clearing Operations [Line Items]
Default funds and margin deposits assets	$ 2,323	$ 5,842
Restricted cash and cash equivalents
Clearing Operations [Line Items]
Default funds and margin deposits assets	254	3,120
Demand deposits
Clearing Operations [Line Items]
Default funds and margin deposits assets	233	3,011
Central bank certificates
Clearing Operations [Line Items]
Default funds and margin deposits assets	21	109
Investments
Clearing Operations [Line Items]
Default funds and margin deposits assets	2,069	2,722
European government debt securities
Clearing Operations [Line Items]
Default funds and margin deposits assets	337	292
Reverse repurchase agreements
Clearing Operations [Line Items]
Default funds and margin deposits assets	1,514	2,245
Multilateral development bank debt securities
Clearing Operations [Line Items]
Default funds and margin deposits assets	$ 218	$ 185