AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
AOCI, Net of Tax [Roll Forward]
OCI	$ 1,020	$ (4,931)
Pension and OPEB Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,535)	(86)
OCI before reclassifications, net of tax	(26)	2
OCI	(14)	8
AOCI, ending balance	(1,549)	(78)
Pension and OPEB Costs | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	16	8
Tax effect	4	2
Amounts reclassified, net of tax	12	6
Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(78)	(9)
OCI before reclassifications, net of tax	125	0
OCI	125	5
AOCI, ending balance	47	(4)
Cash Flow Hedges | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	0	6
Tax effect	0	1
Amounts reclassified, net of tax	0	5
AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(9,395)	(1,510)
OCI before reclassifications, net of tax	903	(5,036)
AFS Securities transferred to HTM, net of tax		2,872
OCI	853	(4,989)
AOCI, ending balance	(8,542)	(3,627)
AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	(65)	61
Tax effect	(15)	14
Amounts reclassified, net of tax	(50)	47
HTM Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(2,588)	0
OCI before reclassifications, net of tax	0	0
AFS Securities transferred to HTM, net of tax		(2,872)
OCI	55	44
AOCI, ending balance	(2,533)	(2,828)
HTM Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	70	57
Tax effect	15	13
Amounts reclassified, net of tax	55	44
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(5)	1
OCI before reclassifications, net of tax	1	1
OCI	1	1
AOCI, ending balance	(4)	2
Other, net | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	0	0
Tax effect	0	0
Amounts reclassified, net of tax	0	0
Total
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(13,601)	(1,604)
OCI before reclassifications, net of tax	1,003	(5,033)
OCI	1,020	(4,931)
AOCI, ending balance	(12,581)	(6,535)
Total | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	21	132
Tax effect	4	30
Amounts reclassified, net of tax	$ 17	$ 102