Commitments and Contingent Liabilities (Summary of Off-Balance Sheet Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 335,823.7	$ 330,600.4
OVER ONE YEAR	18,245.1	18,825.8
TOTAL	354,068.8	349,426.2
Undrawn Commitments
Loss Contingencies [Line Items]
Commitments, participated to others	116.1	175.1
Securities Lent with Indemnification
Loss Contingencies [Line Items]
ONE YEAR AND LESS	177,081.7	170,738.8
OVER ONE YEAR	0.0	0.0
TOTAL	177,081.7	170,738.8
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	69.3	68.1
Standby Letter of Credit and Financial Guarantee
Loss Contingencies [Line Items]
Guarantor obligations, current carrying value	146,600.0	147,800.0
Undrawn Commitments
Loss Contingencies [Line Items]
ONE YEAR AND LESS	11,240.4	10,959.6
OVER ONE YEAR	17,543.9	18,154.7
TOTAL	28,784.3	29,114.3
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	147,476.1	148,883.9
OVER ONE YEAR	701.2	671.0
TOTAL	148,177.3	149,554.9
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	25.5	18.1
OVER ONE YEAR	0.0	0.1
TOTAL	$ 25.5	$ 18.2