Deposits and Borrowings - Long-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Total long-term debt	$ 41,200	$ 44,989
Total short-term borrowings and long-term debt	41,773	45,551
Time deposits, at or above FDIC insurance limit	12,600	15,200
Deposit liability, uninsured	8,800	10,100
Senior and subordinated notes	29,459	30,696
Euro
Debt Instrument [Line Items]
Senior and subordinated notes	$ 494	473
Securitized debt obligations
Debt Instrument [Line Items]
Weighted-Average Interest Rate	3.59%
Carrying value	$ 11,716	14,264
Total senior and subordinated notes
Debt Instrument [Line Items]
Carrying value	$ 29,459	30,696
Senior notes | Fixed unsecured senior debt
Debt Instrument [Line Items]
Weighted-Average Interest Rate	5.09%
Carrying value	$ 23,865	26,930
Subordinated notes | Fixed unsecured subordinated debt
Debt Instrument [Line Items]
Weighted-Average Interest Rate	4.37%
Carrying value	$ 5,594	3,766
Other long-term borrowings
Debt Instrument [Line Items]
Weighted-Average Interest Rate	5.93%
Carrying value	$ 25	$ 29
Minimum | Securitized debt obligations
Debt Instrument [Line Items]
Stated Interest Rates	0.77%
Minimum | Senior notes | Fixed unsecured senior debt
Debt Instrument [Line Items]
Stated Interest Rates	1.65%
Minimum | Subordinated notes | Fixed unsecured subordinated debt
Debt Instrument [Line Items]
Stated Interest Rates	2.36%
Minimum | Other long-term borrowings
Debt Instrument [Line Items]
Stated Interest Rates	1.46%
Maximum | Securitized debt obligations
Debt Instrument [Line Items]
Stated Interest Rates	5.91%
Maximum | Senior notes | Fixed unsecured senior debt
Debt Instrument [Line Items]
Stated Interest Rates	7.62%
Maximum | Subordinated notes | Fixed unsecured subordinated debt
Debt Instrument [Line Items]
Stated Interest Rates	6.18%
Maximum | Other long-term borrowings
Debt Instrument [Line Items]
Stated Interest Rates	9.91%