Derivatives - Undesignated Hedges (Parenthetical) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Cash Flow and Fair Value Hedges
Foreign exchange gains/(losses) on settlement assets and obligations, cash balances, and other assets and liabilities	$ (13.0)	$ 25.7	$ (24.3)	$ 37.9

Represents Foreign Exchange Gain Loss on Settlement Assets and Obligations, Other Assets and Other Liabilities and Cash Balances

No definition available.

Name:	wu_ForeignExchangeGainLossOnSettlementAssetsAndObligationsOtherAssetsAndOtherLiabilitiesAndCashBalances
Namespace Prefix:	wu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration