Commitments and Contingent Liabilities (Narrative) (Details)					3 Months Ended			6 Months Ended	12 Months Ended
	May 03, 2024 shares	Apr. 08, 2024 exchange_offer shares	Mar. 05, 2024 EUR (€)	Sep. 13, 2023	Jun. 30, 2024 USD ($) $ / shares	Jun. 30, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($)	Jun. 30, 2024 USD ($) $ / shares	Dec. 31, 2015 trust
Loss Contingencies [Line Items]
Minimum securities lending related collateral percentage					100.00%	100.00%		100.00%
Commitments and letters of credit					$ 288,133,400,000	$ 288,133,400,000	$ 285,387,400,000	$ 288,133,400,000
Resell agreements, period end amounts excluding effects of agreements reported net by counterparty					20,600,000,000	20,600,000,000	27,700,000,000	20,600,000,000
Repurchase agreement counterparty, amount at risk					0	0	0	0
FDIC, special assessment					2,300,000			14,700,000
Loss contingency accrual					$ 0	$ 0		0
Escrow deposit								$ 2,800,000,000
Common stock, convertible, conversion price					1.5875	1.5875		1.5875
Indemnification Agreement
Loss Contingencies [Line Items]
Credit loss liability					$ 0	$ 0	0	$ 0
FDIC Special Assessment
Loss Contingencies [Line Items]
FDIC, special assessment							$ 84,600,000
Loss contingency accrual					99,300,000	99,300,000		99,300,000
Additional cost					2,300,000			14,700,000
Northern Trust Fiduciary Services (Guernsey) Limited
Loss Contingencies [Line Items]
Litigation settlement, amount awarded to other party | €			€ 187,500
Visa Class A Common Stock
Loss Contingencies [Line Items]
Exchange offer program, number of exchange offers | exchange_offer		3
Exchange offer program, length of time between exchanges		12 months
Exchange offer program, claim reduction percentage		50.00%
Visa Class A Common Stock | Period One
Loss Contingencies [Line Items]
Exchange offer program, exchange ratio				0.3333
Exchange offer program, conversion period		45 days
Visa Class A Common Stock | Period Two
Loss Contingencies [Line Items]
Exchange offer program, exchange ratio				0.6666
Exchange offer program, conversion period		90 days
Visa Class A Common Stock | Period Three
Loss Contingencies [Line Items]
Exchange offer program, conversion period		90 days
Visa Class B
Loss Contingencies [Line Items]
Exchange offer program, shares tendered (in shares) | shares		4,100,000
Carryover basis					$ 0	0		0
Conversion of stock, amount converted						$ 860,400,000
Visa Class B-2 Shares
Loss Contingencies [Line Items]
Exchange offer program, shares received upon expiration (in shares) | shares	2,100,000
Visa Class C shares
Loss Contingencies [Line Items]
Exchange offer program, shares received upon expiration (in shares) | shares	819,500
Number of shares sold (in shares) | shares						546,300
Realized gain recorded						$ 607,000,000		607,000,000.0
Unrealized gain recorded at fair value in Other Assets						$ 286,800,000		$ 286,800,000
Visa Class B Convertible Into Visa Class A | Visa
Loss Contingencies [Line Items]
Share price (in USD) | $ / shares					$ 262.47	$ 262.47		$ 262.47
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	$ 0		$ 0
Upper Limit
Loss Contingencies [Line Items]
Possible loss in future periods in excess of accrual					$ 20,000,000	$ 20,000,000		$ 20,000,000