Clearing Operations (Investment Policy) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Clearing Operations [Line Items]
Total	$ 7,299
Demand deposits
Clearing Operations [Line Items]
Total	1,069	$ 1,328
Central bank certificates
Clearing Operations [Line Items]
Total	1,024	896
European government debt securities
Clearing Operations [Line Items]
Total	388	508
Reverse repurchase agreements
Clearing Operations [Line Items]
Total	482	116
Supranationals and state owned enterprise debt securities
Clearing Operations [Line Items]
Total	278	148
Nordic Clearing Members Cash Contributions [Member]
Clearing Operations [Line Items]
Total	$ 3,241	$ 2,996