Commitments and Contingent Liabilities - Summary of Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 186,533.0	$ 170,021.2
OVER ONE YEAR	18,612.4	18,441.5
TOTAL	205,145.4	188,462.7
Undrawn Commitments to Extend Credit
Loss Contingencies [Line Items]
Commitments, participated to others	342.5	384.7
Custody Securities Lent with Indemnification
Loss Contingencies [Line Items]
ONE YEAR AND LESS	175,509.6	157,478.0
OVER ONE YEAR	0.0	0.0
TOTAL	175,509.6	157,478.0
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	33.3	24.2
Undrawn Commitments to Extend Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	9,676.4	11,260.5
OVER ONE YEAR	18,209.5	17,678.0
TOTAL	27,885.9	28,938.5
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	1,284.9	1,228.1
OVER ONE YEAR	402.9	763.5
TOTAL	1,687.8	1,991.6
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	62.1	54.6
OVER ONE YEAR	0.0	0.0
TOTAL	$ 62.1	$ 54.6