Financial Derivatives (Derivative Assets and Liabilities Offsetting) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	$ 6,447	$ 6,533
Derivative Asset, Fair Value Offset Amount	919	720
Derivative asset, cash collateral	859	1,434
Derivative Asset, Net	4,669	4,379
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	389	532
Derivative Asset, Fair Value, Amount Offset Against Collateral	4,280	3,847
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	3,719	2,756
Derivative liability, fair value offset amount	919	720
Derivative liability, cash collateral	2,078	1,452
Derivative liability, net	722	584
Derivative liability, fair value of collateral
Derivative liability, fair value, amount offset against collateral	722	584
Interest Rate Contracts | Over-the-counter cleared
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	27	48
Derivative Asset, Net	27	48
Derivative Asset, Fair Value, Amount Offset Against Collateral	27	48
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	21	42
Derivative liability, net	21	42
Derivative liability, fair value, amount offset against collateral	21	42
Interest Rate Contracts | Over-the-counter
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	4,697	5,803
Derivative Asset, Fair Value Offset Amount	556	430
Derivative asset, cash collateral	830	1,426
Derivative Asset, Net	3,311	3,947
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	388	531
Derivative Asset, Fair Value, Amount Offset Against Collateral	2,923	3,416
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	1,756	1,740
Derivative liability, fair value offset amount	597	462
Derivative liability, cash collateral	949	1,179
Derivative liability, net	210	99
Derivative liability, fair value, amount offset against collateral	210	99
Commodity contracts:
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	1,469	411
Derivative Asset, Fair Value Offset Amount	250	209
Derivative asset, cash collateral	15	4
Derivative Asset, Net	1,204	198
Derivative Asset, Fair Value, Amount Offset Against Collateral	1,204	198
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	1,485	384
Derivative liability, fair value offset amount	253	182
Derivative liability, cash collateral	997	103
Derivative liability, net	235	99
Derivative liability, fair value, amount offset against collateral	235	99
Foreign exchange contracts and other
Offsetting Derivative Assets [Abstract]
Derivative asset, gross fair value	254	271
Derivative Asset, Fair Value Offset Amount	113	81
Derivative asset, cash collateral	14	4
Derivative Asset, Net	127	186
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	1	1
Derivative Asset, Fair Value, Amount Offset Against Collateral	126	185
Offsetting Derivative Liabilities [Abstract]
Derivative liability, gross fair value	457	590
Derivative liability, fair value offset amount	69	76
Derivative liability, cash collateral	132	170
Derivative liability, net	256	344
Derivative liability, fair value, amount offset against collateral	$ 256	$ 344