Commitments and Contingent Liabilities - Summary of Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 189,438.7	$ 170,021.2
OVER ONE YEAR	18,337.0	18,441.5
TOTAL	207,775.7	188,462.7
Undrawn Commitments to Extend Credit
Loss Contingencies [Line Items]
Commitments, participated to others	404.2	384.7
Custody Securities Lent with Indemnification
Loss Contingencies [Line Items]
ONE YEAR AND LESS	176,378.0	157,478.0
OVER ONE YEAR	0.0	0.0
TOTAL	176,378.0	157,478.0
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	23.8	24.2
Undrawn Commitments to Extend Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	11,519.7	11,260.5
OVER ONE YEAR	18,016.0	17,678.0
TOTAL	29,535.7	28,938.5
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	1,474.8	1,228.1
OVER ONE YEAR	321.0	763.5
TOTAL	1,795.8	1,991.6
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	66.2	54.6
OVER ONE YEAR	0.0	0.0
TOTAL	$ 66.2	$ 54.6