AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Amounts reclassified from AOCI:
OCI	$ (2,320)	$ 1,560	$ 871
Pension and OPEB Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(875)	(1,122)	(1,164)
OCI before reclassifications, net of tax	767	190	(42)
Amounts reclassified from AOCI:
OCI	789	247	42
AOCI, ending balance	(86)	(875)	(1,122)
Pension and OPEB Costs | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	29	75	111
Tax effect	7	18	27
Amounts reclassified, net of tax	22	57	84
Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(64)	(101)	(31)
OCI before reclassifications, net of tax	0	1	(89)
Amounts reclassified from AOCI:
OCI	55	37	(70)
AOCI, ending balance	(9)	(64)	(101)
Cash Flow Hedges | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	72	48	25
Tax effect	17	12	6
Amounts reclassified, net of tax	55	36	19
AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	1,654	380	(500)
OCI before reclassifications, net of tax	(3,459)	1,298	790
Amounts reclassified from AOCI:
OCI	(3,164)	1,274	880
AOCI, ending balance	(1,510)	1,654	380
AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	384	(32)	119
Tax effect	89	(8)	29
Amounts reclassified, net of tax	295	(24)	90
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	1	(1)	(20)
OCI before reclassifications, net of tax	0	2	18
Amounts reclassified from AOCI:
OCI	0	2	19
AOCI, ending balance	1	1	(1)
Other, net | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	0	0	1
Tax effect	0	0	0
Amounts reclassified, net of tax	0	0	1
Total
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	716	(844)	(1,715)
OCI before reclassifications, net of tax	(2,692)	1,491	677
Amounts reclassified from AOCI:
OCI	(2,320)	1,560	871
AOCI, ending balance	(1,604)	716	(844)
Total | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	485	91	256
Tax effect	113	22	62
Amounts reclassified, net of tax	$ 372	$ 69	$ 194