Derivative instruments (Narrative) (Detail 1) $ in Billions	12 Months Ended
	Dec. 31, 2020 USD ($)
Disclosure Of Derivative Instruments [Line Items]
Additional contractual obligations related to OTC derivatives required in the event of a one-notch reduction in long-term credit ratings of UBS	$ 0.0
Additional contractual obligations related to OTC derivatives required in the event of a two-notch reduction in long-term credit ratings of UBS	0.5
Additional contractual obligations related to OTC derivatives required in the event of a three-notch reduction in long-term credit ratings of UBS	1.1
UBS AG
Disclosure Of Derivative Instruments [Line Items]
Additional contractual obligations related to OTC derivatives required in the event of a one-notch reduction in long-term credit ratings of UBS	0.0
Additional contractual obligations related to OTC derivatives required in the event of a two-notch reduction in long-term credit ratings of UBS	0.5
Additional contractual obligations related to OTC derivatives required in the event of a three-notch reduction in long-term credit ratings of UBS	$ 1.1