Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	$ 1,040	$ 849
Securities available for sale	21,843	19,428
Loans, net of unearned income (residential)	94,646	89,552
Netting adjustments	(473)	(333)
Total derivative assets	780	531
LIABILITIES MEASURED ON A RECURRING BASIS
Netting adjustments	(335)	(337)
U.S. Treasury, Agencies, and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	334	147
State and municpal bonds [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	4	7
Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	11	20
Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,714	2,105
Other Mortgage-Backed Securities [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	6,997	3,187
Fair Value, Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	995	824
Commercial loans	45	25
Total trading account assets	1,040	849
Securities available for sale	21,843	19,428
Total other investments	90	115
Loans, net of unearned income (residential)	4	3
Loans held for sale	140	54
Derivative assets	1,253	864
Netting adjustments	(473)	(333)
Total derivative assets	780	531
Total assets on a recurring basis at fair value	23,897	20,980
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	903	930
Fair Value, Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	12,783	13,962
Fair Value, Recurring [Member] | U.S. Treasury, Agencies, and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	843	578
Securities available for sale	334	147
Fair Value, Recurring [Member] | State and municpal bonds [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	30	60
Securities available for sale	4	7
Fair Value, Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	44	22
Securities available for sale	11	20
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	6,997	3,187
Fair Value, Recurring [Member] | Principal Direct Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	1	1
Fair Value, Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	69	97
Fair Value, Recurring [Member] | Equity Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	12	8
Fair Value, Recurring [Member] | Equity Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	21	18
Fair Value, Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	78	164
Fair Value, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,714	2,105
Fair Value, Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	705	544
Fair Value, Recurring [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	533	723
Netting adjustments	(335)	(337)
Total derivative liabilities	198	386
Fair Value, Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	963	415
Fair Value, Recurring [Member] | Interest Rate [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	253	297
Fair Value, Recurring [Member] | Foreign Exchange Contract [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	67	106
Fair Value, Recurring [Member] | Foreign Exchange Contract [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	60	95
Fair Value, Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	208	333
Fair Value, Recurring [Member] | Commodity [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	200	323
Fair Value, Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	1	1
Fair Value, Recurring [Member] | Credit [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	10	1
Fair Value, Recurring [Member] | Other [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	14	9
Fair Value, Recurring [Member] | Other [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	10	7
Level 1 [Member] | Fair Value, Recurring [Member]
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	0	0
Loans, net of unearned income (residential)	0	0
Loans held for sale	0	0
Derivative assets	49	70
Netting adjustments	0	0
Total derivative assets	49	70
Total assets on a recurring basis at fair value	49	70
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	62	72
Level 1 [Member] | Fair Value, Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | U.S. Treasury, Agencies, and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | State and municpal bonds [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Principal Direct Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Equity Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Equity Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	19	14
Level 1 [Member] | Fair Value, Recurring [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	43	58
Netting adjustments	0	0
Total derivative liabilities	43	58
Level 1 [Member] | Fair Value, Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Interest Rate [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Foreign Exchange Contract [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	49	70
Level 1 [Member] | Fair Value, Recurring [Member] | Foreign Exchange Contract [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	43	58
Level 1 [Member] | Fair Value, Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Commodity [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Credit [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Other [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 1 [Member] | Fair Value, Recurring [Member] | Other [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 2 [Member] | Fair Value, Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	995	824
Commercial loans	45	25
Total trading account assets	1,040	849
Securities available for sale	21,832	19,408
Total other investments	0	1
Loans, net of unearned income (residential)	0	0
Loans held for sale	140	54
Derivative assets	1,176	786
Netting adjustments	0	0
Total derivative assets	1,176	786
Total assets on a recurring basis at fair value	24,188	21,098
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	1,167	1,195
Level 2 [Member] | Fair Value, Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	12,783	13,962
Level 2 [Member] | Fair Value, Recurring [Member] | U.S. Treasury, Agencies, and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	843	578
Securities available for sale	334	147
Level 2 [Member] | Fair Value, Recurring [Member] | State and municpal bonds [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	30	60
Securities available for sale	4	7
Level 2 [Member] | Fair Value, Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	44	22
Securities available for sale	0	0
Level 2 [Member] | Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	6,997	3,187
Level 2 [Member] | Fair Value, Recurring [Member] | Principal Direct Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 [Member] | Fair Value, Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	0
Level 2 [Member] | Fair Value, Recurring [Member] | Equity Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	1
Level 2 [Member] | Fair Value, Recurring [Member] | Equity Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	0	1
Level 2 [Member] | Fair Value, Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	78	164
Level 2 [Member] | Fair Value, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	1,714	2,105
Level 2 [Member] | Fair Value, Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	686	530
Level 2 [Member] | Fair Value, Recurring [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	481	665
Netting adjustments	0	0
Total derivative liabilities	481	665
Level 2 [Member] | Fair Value, Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	941	410
Level 2 [Member] | Fair Value, Recurring [Member] | Interest Rate [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	253	297
Level 2 [Member] | Fair Value, Recurring [Member] | Foreign Exchange Contract [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	18	36
Level 2 [Member] | Fair Value, Recurring [Member] | Foreign Exchange Contract [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	17	37
Level 2 [Member] | Fair Value, Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	208	333
Level 2 [Member] | Fair Value, Recurring [Member] | Commodity [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	200	323
Level 2 [Member] | Fair Value, Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	1
Level 2 [Member] | Fair Value, Recurring [Member] | Credit [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	1	1
Level 2 [Member] | Fair Value, Recurring [Member] | Other [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	9	6
Level 2 [Member] | Fair Value, Recurring [Member] | Other [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	10	7
Level 3 [Member] | Other [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	5
Level 3 [Member] | Fair Value, Recurring [Member]
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	11	20
Total other investments	13	8
Loans, net of unearned income (residential)	4	3
Loans held for sale	0	0
Derivative assets	28	8
Netting adjustments	0	0
Total derivative assets	28	8
Total assets on a recurring basis at fair value	56	39
LIABILITIES MEASURED ON A RECURRING BASIS
Total liabilities on a recurring basis at fair value	9	0
Level 3 [Member] | Fair Value, Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | U.S. Treasury, Agencies, and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | State and municpal bonds [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Securities available for sale	11	20
Level 3 [Member] | Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Principal Direct Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	1	1
Level 3 [Member] | Fair Value, Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	1	1
Level 3 [Member] | Fair Value, Recurring [Member] | Equity Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	12	7
Level 3 [Member] | Fair Value, Recurring [Member] | Equity Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	12	7
Level 3 [Member] | Fair Value, Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Other Mortgage-Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Short positions	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	9	0
Netting adjustments	0	0
Total derivative liabilities	9	0
Level 3 [Member] | Fair Value, Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	22	5
Level 3 [Member] | Fair Value, Recurring [Member] | Interest Rate [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Foreign Exchange Contract [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Foreign Exchange Contract [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Commodity [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Level 3 [Member] | Fair Value, Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	1	0
Level 3 [Member] | Fair Value, Recurring [Member] | Credit [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	9	0
Level 3 [Member] | Fair Value, Recurring [Member] | Other [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets		3
Level 3 [Member] | Fair Value, Recurring [Member] | Other [Member] | Long Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	0	0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Principal Indirect Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	68	96
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Equity Investments Direct, NAV [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	1	1
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Equity Investments Indirect, NAV [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	$ 8	$ 9