Commitments and Contingent Liabilities - Summary of Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 330,600.4	$ 267,669.9
OVER ONE YEAR	18,825.8	17,783.5
TOTAL	349,426.2	285,453.4
Legally Binding Commitments to Extend Credit
Loss Contingencies [Line Items]
Commitments, participated to others	175.1	268.5
Financial Guarantee
Loss Contingencies [Line Items]
ONE YEAR AND LESS	170,738.8	144,543.7
OVER ONE YEAR	0.0	0.0
TOTAL	170,738.8	144,543.7
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	68.1	109.4
Standby Letter of Credit and Financial Guarantee
Loss Contingencies [Line Items]
Guarantor obligations, current carrying value	147,800.0
Guarantees to sponsored member programs		110,800.0
Legally Binding Commitments to Extend Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	10,959.6	10,849.6
OVER ONE YEAR	18,154.7	17,293.2
TOTAL	29,114.3	28,142.8
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	148,883.9	112,256.3
OVER ONE YEAR	671.0	490.1
TOTAL	149,554.9	112,746.4
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	18.1	20.3
OVER ONE YEAR	0.1	0.2
TOTAL	$ 18.2	$ 20.5