Commitments and Contingent Liabilities (Narrative) (Details) shares in Millions		1 Months Ended		9 Months Ended	12 Months Ended
	Sep. 13, 2023 exchangeOffer	Jun. 30, 2016 USD ($) shares	Jun. 30, 2015 USD ($) shares	Sep. 30, 2023 USD ($) shares	Dec. 31, 2015 trust	Dec. 31, 2022 USD ($) shares
Loss Contingencies [Line Items]
Minimum securities lending related collateral percentage				100.00%
Commitments and letters of credit				$ 254,721,600,000		$ 179,758,000,000
Resell agreements, period end amounts excluding effects of agreements reported net by counterparty				19,100,000,000		496,800,000
Repurchase agreement counterparty, amount at risk				0		$ 0
Loss contingency accrual				0
Escrow deposit				$ 2,800,000,000
Visa Class A Common Stock
Loss Contingencies [Line Items]
Potential exchange offer program, number of exchange offers | exchangeOffer	3
Potential exchange offer program, length of time between exchanges	12 months
Potential exchange offer program, claim reduction percentage	50.00%
Visa Class A Common Stock | Period One
Loss Contingencies [Line Items]
Potential exchange offer program, exchange ratio	0.3333
Potential exchange offer program, conversion period	45 days
Visa Class A Common Stock | Period Two
Loss Contingencies [Line Items]
Potential exchange offer program, exchange ratio	0.6666
Potential exchange offer program, conversion period	90 days
Visa Class A Common Stock | Period Three
Loss Contingencies [Line Items]
Potential exchange offer program, conversion period	90 days
Visa Class B
Loss Contingencies [Line Items]
Visa redemption gain		$ 123,100,000	$ 99,900,000
Shares issued (in shares) | shares		1.1	1.0
Common stock shares held (in shares) | shares				4.1		4.1
Remaining Visa shares held by Northern Trust, original cost basis				$ 0		$ 0
Northern Trust Fiduciary Services (Guernsey) Limited | Subsidiaries
Loss Contingencies [Line Items]
Number of administrated trusts serving as trustee on | trust					2
Lower Limit
Loss Contingencies [Line Items]
Possible loss in future periods in excess of accrual				0
Upper Limit
Loss Contingencies [Line Items]
Possible loss in future periods in excess of accrual				25,000,000
Indemnification Agreement
Loss Contingencies [Line Items]
Credit loss liability				0		$ 0
FDIC Special Assessment
Loss Contingencies [Line Items]
Possible loss in future periods in excess of accrual				$ 80,000,000