Fair Value of Assets and Liabilities (Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	$ 2,213	$ 1,906
Netting	(13,233)	(21,367)
Total derivative liabilities	1,185	792
Netting	(16,466)	(17,475)
Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	11,838	19,190
Total derivative liabilities	15,219	13,508
Currency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	990	832
Total derivative liabilities	1,162	763
Credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	168	63
Total derivative liabilities	0	28
Currency/Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	1,758	1,415
Total derivative liabilities	525	1,638
Equity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	692	1,773
Total derivative liabilities	745	2,330
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	148	227
Total derivative liabilities	60	30
Level 1 | Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	6	99
Total derivative liabilities	14	5
Level 1 | Currency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 1 | Credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 1 | Currency/Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 1 | Equity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	142	128
Total derivative liabilities	46	25
Level 1 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	15,297	23,046
Total derivative liabilities	17,591	18,237
Level 2 | Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	11,831	19,091
Total derivative liabilities	15,205	13,503
Level 2 | Currency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	990	832
Total derivative liabilities	1,162	763
Level 2 | Credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	168	63
Total derivative liabilities	0	28
Level 2 | Currency/Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	1,758	1,415
Total derivative liabilities	525	1,638
Level 2 | Equity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	550	1,645
Total derivative liabilities	699	2,305
Level 2 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	1	0
Total derivative liabilities	0	0
Level 3 | Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	1	0
Total derivative liabilities	0	0
Level 3 | Currency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 3 | Credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 3 | Currency/Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 3 | Equity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Level 3 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Netting	$ 3,233	$ (3,892)