Commitments and Contingent Liabilities - Summary of Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 170,021.2	$ 147,186.0
OVER ONE YEAR	18,441.5	17,751.9
TOTAL	188,462.7	164,937.9
Legally Binding Commitments to Extend Credit
Loss Contingencies [Line Items]
Commitments, participated to others	384.7	243.6
Custody Securities Lent with Indemnification
Loss Contingencies [Line Items]
ONE YEAR AND LESS	157,478.0	138,085.9
OVER ONE YEAR	0.0	0.0
TOTAL	157,478.0	138,085.9
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	24.2	44.5
Legally Binding Commitments to Extend Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	11,260.5	7,500.2
OVER ONE YEAR	17,678.0	16,906.0
TOTAL	28,938.5	24,406.2
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	1,228.1	1,567.6
OVER ONE YEAR	763.5	845.9
TOTAL	1,991.6	2,413.5
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	54.6	32.3
OVER ONE YEAR	0.0	0.0
TOTAL	$ 54.6	$ 32.3