Commitments, Contingent Liabilities and Guarantees - Visa Funding and Bancorp Cash Payments (Details) - USD ($) $ in Millions		3 Months Ended
	Apr. 08, 2025	Sep. 30, 2024	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021	Sep. 30, 2019	Jun. 30, 2018	Sep. 30, 2014	Sep. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Mar. 31, 2025	Dec. 31, 2008
Visa Funding
Loss Contingencies
Visa Funding Amount		$ 1,500	$ 150	$ 500	$ 350	$ 600	$ 250	$ 300	$ 600	$ 450	$ 150	$ 1,565	$ 400	$ 800	$ 500	$ 375	$ 3,000
Bancorp Cash Payment
Loss Contingencies
Bancorp Cash Payment Amount		$ 65	$ 6	$ 21	$ 15	$ 25	$ 11	$ 12	$ 26	$ 18	$ 6	$ 75	$ 19	$ 35	$ 20
Bancorp Cash Payment | Subsequent Event
Loss Contingencies
Bancorp Cash Payment Amount	$ 15