Commitments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Commitments [Line Items]
Financing commitments to trade finance clients that are cancelable only after a notice period, amount	$ 175.0	$ 172.0
Deferred Purchase Agreements
Commitments [Line Items]
DPA, borrowings by client	131.2
DPA credit protection provided to clients	1,492.0	1,966.0
DPA credit line agreements net of deferred purchase agreement credit protection	$ 64.0	$ 94.0
Maximum
Commitments [Line Items]
Typical notice period	90 days
Maximum | Deferred Purchase Agreements
Commitments [Line Items]
DPA credit line agreements, cancellation notice period	90 days