Fair Value - Schedule of Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	$ 780	$ 773
Available-for-sale investment securities:	56,755	44,526
Bank-owned life insurance	5,875	5,307
Derivative asset, collateral, cash offset	903	3,904
Derivative liability, collateral, cash offset	3,221	1,413
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	141	306
Direct obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	18,589	8,301
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	10,949	10,755
Total U.S. Treasury and federal agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	29,538	19,056
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,356	1,857
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,238	2,137
Non-U.S. sovereign, supranational and non-U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	16,161	15,100
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	3,044	2,735
Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	23,799	21,829
Student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	101	114
Collateralized loan obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,612	2,527
Non-agency CMBS and RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	136	249
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	91	90
Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,940	2,980
State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	337	355
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	780	773
Available-for-sale investment securities:	56,755	44,526
Derivative asset, Impact of Netting	(9,889)	(14,400)
Bank-owned life insurance	5,875	5,307
Other	661	651
Other, Impact of Netting	0	0
Total	64,071	51,257
Derivative liability, Impact of Netting	(12,207)	(11,909)
Derivative liabilities	4,035	7,693
Total liabilities carried at fair value	4,035	7,693
Recurring | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, Impact of Netting	(9,886)	(14,387)
Bank-owned life insurance	5,868	5,307
Derivative liability, Impact of Netting	(12,207)	(11,909)
Derivative liabilities	3,866	7,507
Recurring | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, Impact of Netting	(3)	(13)
Bank-owned life insurance	7	0
Derivative liability, Impact of Netting	0	0
Derivative liabilities	0	4
Recurring | Other derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, Impact of Netting	0	0
Derivative liabilities	169	182
Recurring | U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	35	36
Recurring | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	130	138
Recurring | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	615	599
Available-for-sale investment securities:	141	306
Recurring | Direct obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	18,589	8,301
Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	10,949	10,755
Recurring | Total U.S. Treasury and federal agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	29,538	19,056
Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,356	1,857
Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,238	2,137
Recurring | Non-U.S. sovereign, supranational and non-U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	16,161	15,100
Recurring | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	3,044	2,735
Recurring | Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	23,799	21,829
Recurring | Student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	101	114
Recurring | Collateralized loan obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,612	2,527
Recurring | Non-agency CMBS and RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	136	249
Recurring | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	91	90
Recurring | Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,940	2,980
Recurring | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	337	355
Recurring | Quoted Market Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	35	36
Available-for-sale investment securities:	18,589	8,301
Derivative asset	12	0
Other	18	11
Total	18,654	8,348
Derivative liability	0	5
Total liabilities carried at fair value	0	5
Recurring | Quoted Market Prices in Active Markets (Level 1) | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	4	0
Derivative liability	0	1
Recurring | Quoted Market Prices in Active Markets (Level 1) | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	8	0
Derivative liability	0	4
Recurring | Quoted Market Prices in Active Markets (Level 1) | Other derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	35	36
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	0	0
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Direct obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	18,589	8,301
Recurring | Quoted Market Prices in Active Markets (Level 1) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Total U.S. Treasury and federal agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	18,589	8,301
Recurring | Quoted Market Prices in Active Markets (Level 1) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-U.S. sovereign, supranational and non-U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Collateralized loan obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-agency CMBS and RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Quoted Market Prices in Active Markets (Level 1) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	745	737
Available-for-sale investment securities:	38,166	36,225
Derivative asset	15,749	19,703
Other	643	640
Total	55,303	57,305
Derivative liability	16,242	19,596
Total liabilities carried at fair value	16,242	19,596
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	15,747	19,690
Derivative liability	16,073	19,414
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	2	13
Derivative liability	0	0
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Other derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	169	182
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	0	0
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	130	138
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	615	599
Available-for-sale investment securities:	141	306
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Direct obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	10,949	10,755
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Total U.S. Treasury and federal agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	10,949	10,755
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,356	1,857
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,238	2,137
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Non-U.S. sovereign, supranational and non-U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	16,161	15,100
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	3,044	2,735
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	23,799	21,829
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	101	114
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Collateralized loan obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,612	2,527
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Non-agency CMBS and RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	136	249
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	91	90
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	2,940	2,980
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	337	355
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	0	0
Available-for-sale investment securities:	0	0
Derivative asset	3	4
Other	0	0
Total	3	4
Derivative liability	0	1
Total liabilities carried at fair value	0	1
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	3	4
Derivative liability	0	1
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Derivative liability	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	0	0
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Direct obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Total U.S. Treasury and federal agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. sovereign, supranational and non-U.S. agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized loan obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-agency CMBS and RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	0	0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities:	$ 0	$ 0