Commitments and Contingent Liabilities (Summary of Off-Balance Sheet Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 303,394.3	$ 267,669.9
OVER ONE YEAR	17,838.3	17,783.5
TOTAL	321,232.6	285,453.4
Undrawn Commitments
Loss Contingencies [Line Items]
Commitments, participated to others	221.1	268.5
Securities Lent with Indemnification
Loss Contingencies [Line Items]
ONE YEAR AND LESS	167,606.5	144,543.7
OVER ONE YEAR	0.0	0.0
TOTAL	167,606.5	144,543.7
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	69.1	109.4
Standby Letter of Credit and Financial Guarantee
Loss Contingencies [Line Items]
Guarantor obligations, current carrying value	124,000.0	110,800.0
Undrawn Commitments
Loss Contingencies [Line Items]
ONE YEAR AND LESS	10,276.9	10,849.6
OVER ONE YEAR	17,504.9	17,293.2
TOTAL	27,781.8	28,142.8
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	125,473.6	112,256.3
OVER ONE YEAR	333.2	490.1
TOTAL	125,806.8	112,746.4
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	37.3	20.3
OVER ONE YEAR	0.2	0.2
TOTAL	$ 37.5	$ 20.5