Commitments and Contingent Liabilities - Summary of Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2021
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 162,025.4	$ 183,566.4
OVER ONE YEAR	17,732.6	18,410.2
TOTAL	179,758.0	201,976.6
Legally Binding Commitments to Extend Credit
Loss Contingencies [Line Items]
Commitments, participated to others	266.6	366.6
Financial Guarantee
Loss Contingencies [Line Items]
ONE YEAR AND LESS	130,311.0	170,445.3
OVER ONE YEAR	0.0	0.0
TOTAL	130,311.0	170,445.3
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	35.1	30.5
Standby Letter of Credit and Financial Guarantee
Loss Contingencies [Line Items]
Guarantor obligations, current carrying value	16,300.0
Guarantees to sponsored member programs			$ 2,300.0
Legally Binding Commitments to Extend Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	13,639.2	9,567.0
OVER ONE YEAR	17,321.4	17,855.2
TOTAL	30,960.6	27,422.2
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	17,553.0	3,485.6
OVER ONE YEAR	409.9	553.9
TOTAL	17,962.9	4,039.5
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	25.4	68.5
OVER ONE YEAR	1.3	1.1
TOTAL	26.7	69.6
Unsettled Reverse Repurchase Agreements
Loss Contingencies [Line Items]
ONE YEAR AND LESS	496.8	0.0
OVER ONE YEAR	0.0	0.0
TOTAL	$ 496.8	$ 0.0