Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	$ 851	$ 735
Securities available for sale	34,638	27,556
Loans, net of unearned income (residential)	100,730	101,185
Derivative assets, netting adjustments	(251)	(380)
Total derivative assets	2,160	1,798
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, netting adjustments	(1,428)	(675)
Other
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	13
Recurring
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	836	717
Commercial loans	15	18
Total trading account assets	851	735
Securities available for sale	34,638	27,556
Total other investments	93	81
Loans, net of unearned income (residential)	11	11
Loans held for sale (residential)	231	264
Derivative assets, gross	2,411	2,178
Derivative assets, netting adjustments	(251)	(380)
Total derivative assets	2,160	1,798
Accrued income and other assets	0	0
Total assets at fair value	37,984	30,445
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	892	910
Recurring | U.S. Treasury, agencies and corporations
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	631	633
Securities available for sale	4,886	1,000
Recurring | States and political subdivisions
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	86	24
Securities available for sale	0	0
Recurring | Other securities
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	13	13
Securities available for sale	22	13
Recurring | Agency commercial mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	10,478	10,106
Recurring | Principal investments, Direct
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	1	1
Recurring | Principal Investments
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	54	54
Recurring | Equity Investments, Direct
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	20	13
Recurring | Equity Investments
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	39	27
Recurring | Mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	106	47
Recurring | Mortgage-backed securities | Agency residential mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	4,878	2,164
Recurring | Short positions
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	723	759
Recurring | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	1,597	826
Derivative liabilities, netting adjustments	(1,428)	(675)
Total derivative liabilities	169	151
Recurring | Interest rate
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	1,105	1,584
Recurring | Interest rate | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	289	288
Recurring | Foreign exchange
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	87	109
Recurring | Foreign exchange | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	83	103
Recurring | Commodity
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	1,198	426
Recurring | Commodity | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	1,205	408
Recurring | Credit
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	1	1
Recurring | Credit | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	8	11
Recurring | Other
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	20	58
Recurring | Other | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	12	16
Level 1 | Recurring
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Commercial loans	0	0
Total trading account assets	0	0
Securities available for sale	0	0
Total other investments	11	0
Loans, net of unearned income (residential)	0	0
Loans held for sale (residential)	0	0
Derivative assets, gross	65	78
Derivative assets, netting adjustments	0	0
Total derivative assets	65	78
Accrued income and other assets	0	0
Total assets at fair value	76	78
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	273	328
Level 1 | Recurring | U.S. Treasury, agencies and corporations
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 | Recurring | States and political subdivisions
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 | Recurring | Other securities
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 | Recurring | Agency commercial mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 1 | Recurring | Principal investments, Direct
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 | Recurring | Principal Investments
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 | Recurring | Equity Investments, Direct
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	11	0
Level 1 | Recurring | Equity Investments
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	11	0
Level 1 | Recurring | Mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Level 1 | Recurring | Mortgage-backed securities | Agency residential mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 1 | Recurring | Short positions
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	211	256
Level 1 | Recurring | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	62	72
Derivative liabilities, netting adjustments	0	0
Total derivative liabilities	62	72
Level 1 | Recurring | Interest rate
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	0	0
Level 1 | Recurring | Interest rate | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	0	0
Level 1 | Recurring | Foreign exchange
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	65	78
Level 1 | Recurring | Foreign exchange | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	62	72
Level 1 | Recurring | Commodity
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	0	0
Level 1 | Recurring | Commodity | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	0	0
Level 1 | Recurring | Credit
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	0	0
Level 1 | Recurring | Credit | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	0	0
Level 1 | Recurring | Other
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	0	0
Level 1 | Recurring | Other | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	0	0
Level 2 | Recurring
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	836	717
Commercial loans	15	18
Total trading account assets	851	735
Securities available for sale	34,616	27,543
Total other investments	0	0
Loans, net of unearned income (residential)	0	0
Loans held for sale (residential)	231	264
Derivative assets, gross	2,297	2,009
Derivative assets, netting adjustments	0	0
Total derivative assets	2,297	2,009
Accrued income and other assets	0	0
Total assets at fair value	37,995	30,551
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	2,041	1,246
Level 2 | Recurring | U.S. Treasury, agencies and corporations
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	631	633
Securities available for sale	4,886	1,000
Level 2 | Recurring | States and political subdivisions
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	86	24
Securities available for sale	0	0
Level 2 | Recurring | Other securities
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	13	13
Securities available for sale	0	0
Level 2 | Recurring | Agency commercial mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	10,478	10,106
Level 2 | Recurring | Principal investments, Direct
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 | Recurring | Principal Investments
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 | Recurring | Equity Investments, Direct
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 | Recurring | Equity Investments
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 | Recurring | Mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	106	47
Level 2 | Recurring | Mortgage-backed securities | Agency residential mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	4,878	2,164
Level 2 | Recurring | Short positions
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	512	503
Level 2 | Recurring | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	1,529	743
Derivative liabilities, netting adjustments	0	0
Total derivative liabilities	1,529	743
Level 2 | Recurring | Interest rate
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	1,070	1,528
Level 2 | Recurring | Interest rate | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	289	288
Level 2 | Recurring | Foreign exchange
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	22	31
Level 2 | Recurring | Foreign exchange | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	21	31
Level 2 | Recurring | Commodity
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	1,198	424
Level 2 | Recurring | Commodity | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	1,205	408
Level 2 | Recurring | Credit
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	0	0
Level 2 | Recurring | Credit | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	2	0
Level 2 | Recurring | Other
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	7	26
Level 2 | Recurring | Other | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	12	16
Level 3 | Recurring
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Commercial loans	0	0
Total trading account assets	0	0
Securities available for sale	22	13
Total other investments	10	14
Loans, net of unearned income (residential)	11	11
Loans held for sale (residential)	0	0
Derivative assets, gross	49	91
Derivative assets, netting adjustments	0	0
Total derivative assets	49	91
Accrued income and other assets	0	0
Total assets at fair value	92	129
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	6	11
Level 3 | Recurring | U.S. Treasury, agencies and corporations
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 3 | Recurring | States and political subdivisions
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 3 | Recurring | Other securities
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	22	13
Level 3 | Recurring | Agency commercial mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 3 | Recurring | Principal investments, Direct
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	1	1
Level 3 | Recurring | Principal Investments
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	1	1
Level 3 | Recurring | Equity Investments, Direct
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	9	13
Level 3 | Recurring | Equity Investments
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	9	13
Level 3 | Recurring | Mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Level 3 | Recurring | Mortgage-backed securities | Agency residential mortgage-backed securities
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 3 | Recurring | Short positions
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	0	0
Level 3 | Recurring | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	6	11
Derivative liabilities, netting adjustments	0	0
Total derivative liabilities	6	11
Level 3 | Recurring | Interest rate
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	35	56
Level 3 | Recurring | Interest rate | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	0	0
Level 3 | Recurring | Foreign exchange
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	0	0
Level 3 | Recurring | Foreign exchange | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	0	0
Level 3 | Recurring | Commodity
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	0	2
Level 3 | Recurring | Commodity | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	0	0
Level 3 | Recurring | Credit
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross	1	1
Level 3 | Recurring | Credit | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	6	11
Level 3 | Recurring | Other
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets, gross		32
Level 3 | Recurring | Other | Long positions
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities, gross	0	0
Measured at NAV | Recurring | Equity Investments Direct, NAV
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	12	7
Measured at NAV | Recurring | Equity Investments Indirect, NAV
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	7	7
Agency residential collateralized mortgage obligations | Recurring
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	14,374	14,273
Agency residential collateralized mortgage obligations | Level 1 | Recurring
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Agency residential collateralized mortgage obligations | Level 2 | Recurring
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	14,374	14,273
Agency residential collateralized mortgage obligations | Level 3 | Recurring
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Variable Interest Entity, Not Primary Beneficiary | Measured at NAV | Recurring | Principal Investments, Indirect
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	$ 53	$ 53