AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
AOCI, Net of Tax [Roll Forward]
OCI	$ (793)	$ (2,705)	$ 227	$ (7,636)
Pension and OPEB Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,549)	(78)	(1,535)	(86)
OCI before reclassifications, net of tax	(5)	0	(31)	2
OCI	8	5	(6)	13
AOCI, ending balance	(1,541)	(73)	(1,541)	(73)
Pension and OPEB Costs | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	17	8	33	16
Tax effect	4	3	8	5
Amounts reclassified, net of tax	13	5	25	11
Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	47	(4)	(78)	(9)
OCI before reclassifications, net of tax	(321)	46	(196)	46
OCI	(317)	49	(192)	54
AOCI, ending balance	(270)	45	(270)	45
Cash Flow Hedges | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	5	5	5	11
Tax effect	1	2	1	3
Amounts reclassified, net of tax	4	3	4	8
AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(8,542)	(3,627)	(9,395)	(1,510)
OCI before reclassifications, net of tax	(496)	(2,873)	407	(7,909)
AFS Securities transferred to HTM, net of tax				2,872
OCI	(550)	(2,849)	303	(7,838)
AOCI, ending balance	(9,092)	(6,476)	(9,092)	(6,476)
AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	(71)	32	(136)	93
Tax effect	(17)	8	(32)	22
Amounts reclassified, net of tax	(54)	24	(104)	71
HTM Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(2,533)	(2,828)	(2,588)	0
OCI before reclassifications, net of tax	0	0	0	0
AFS Securities transferred to HTM, net of tax				(2,872)
OCI	65	92	120	136
AOCI, ending balance	(2,468)	(2,736)	(2,468)	(2,736)
HTM Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	82	119	152	176
Tax effect	17	27	32	40
Amounts reclassified, net of tax	65	92	120	136
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(4)	2	(5)	1
OCI before reclassifications, net of tax	1	(2)	2	(1)
OCI	1	(2)	2	(1)
AOCI, ending balance	(3)	0	(3)	0
Other, net | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	0	0	0	0
Tax effect	0	0	0	0
Amounts reclassified, net of tax	0	0	0	0
Total
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(12,581)	(6,535)	(13,601)	(1,604)
OCI before reclassifications, net of tax	(821)	(2,829)	182	(7,862)
OCI	(793)	(2,705)	227	(7,636)
AOCI, ending balance	(13,374)	(9,240)	(13,374)	(9,240)
Total | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	33	164	54	296
Tax effect	5	40	9	70
Amounts reclassified, net of tax	$ 28	$ 124	$ 45	$ 226