Financial Derivatives (Derivative Assets and Liabilities Offsetting) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	$ 4,916	$ 6,533
Derivative Asset, Fair Value Offset Amount	904	720
Derivative asset, cash collateral	716	1,434
Derivative Asset, Net	3,296	4,379
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	264	532
Derivative Asset, Fair Value, Amount Offset Against Collateral	3,032	3,847
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	3,023	2,756
Derivative liability, fair value offset amount	904	720
Derivative liability, cash collateral	1,295	1,452
Derivative liability, net	824	584
Derivative liability, fair value of collateral
Derivative liability, fair value, amount offset against collateral	824	584
Interest Rate Contracts | Over-the-counter cleared
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	101	48
Derivative Asset, Net	101	48
Derivative Asset, Fair Value, Amount Offset Against Collateral	101	48
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	158	42
Derivative liability, net	158	42
Derivative liability, fair value, amount offset against collateral	158	42
Interest Rate Contracts | Over-the-counter
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	3,922	5,803
Derivative Asset, Fair Value Offset Amount	620	430
Derivative asset, cash collateral	700	1,426
Derivative Asset, Net	2,602	3,947
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	263	531
Derivative Asset, Fair Value, Amount Offset Against Collateral	2,339	3,416
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	1,770	1,740
Derivative liability, fair value offset amount	653	462
Derivative liability, cash collateral	792	1,179
Derivative liability, net	325	99
Derivative liability, fair value, amount offset against collateral	325	99
Commodity contracts:
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	678	411
Derivative Asset, Fair Value Offset Amount	190	209
Derivative asset, cash collateral	8	4
Derivative Asset, Net	480	198
Derivative Asset, Fair Value, Amount Offset Against Collateral	480	198
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	653	384
Derivative liability, fair value offset amount	184	182
Derivative liability, cash collateral	407	103
Derivative liability, net	62	99
Derivative liability, fair value, amount offset against collateral	62	99
Foreign exchange contracts and other
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	215	271
Derivative Asset, Fair Value Offset Amount	94	81
Derivative asset, cash collateral	8	4
Derivative Asset, Net	113	186
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	1	1
Derivative Asset, Fair Value, Amount Offset Against Collateral	112	185
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	442	590
Derivative liability, fair value offset amount	67	76
Derivative liability, cash collateral	96	170
Derivative liability, net	279	344
Derivative liability, fair value, amount offset against collateral	$ 279	$ 344