AOCI (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Amounts reclassified from AOCI:
OCI	$ (51)	$ 302	$ 1,691	$ 596
Pension and OPEB Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,107)	(1,147)	(1,122)	(1,164)
OCI before reclassifications, net of tax	(1)	0	(1)	0
Amounts reclassified from AOCI:
OCI	14	19	29	36
AOCI, ending balance	(1,093)	(1,128)	(1,093)	(1,128)
Pension and OPEB Costs \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	20	24	40	47
Tax effect	5	5	10	11
Amounts reclassified, net of tax	15	19	30	36
Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(90)	(65)	(101)	(31)
OCI before reclassifications, net of tax	0	(61)	0	(91)
Amounts reclassified from AOCI:
OCI	11	(59)	22	(93)
AOCI, ending balance	(79)	(124)	(79)	(124)
Cash Flow Hedges \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	14	2	29	(3)
Tax effect	3	0	7	(1)
Amounts reclassified, net of tax	11	2	22	(2)
AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	2,101	(191)	380	(500)
OCI before reclassifications, net of tax	101	346	1,791	660
Amounts reclassified from AOCI:
OCI	(79)	342	1,642	651
AOCI, ending balance	2,022	151	2,022	151
AFS Securities \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	(237)	(6)	(196)	(12)
Tax effect	(57)	(2)	(47)	(3)
Amounts reclassified, net of tax	(180)	(4)	(149)	(9)
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(6)	(18)	(1)	(20)
OCI before reclassifications, net of tax	3	0	(2)	2
Amounts reclassified from AOCI:
OCI	3	0	(2)	2
AOCI, ending balance	(3)	(18)	(3)	(18)
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	898	(1,421)	(844)	(1,715)
OCI before reclassifications, net of tax	103	285	1,788	571
Amounts reclassified from AOCI:
OCI	(51)	302	1,691	596
AOCI, ending balance	847	(1,119)	847	(1,119)
Total \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	(203)	20	(127)	32
Tax effect	(49)	3	(30)	7
Amounts reclassified, net of tax	$ (154)	$ 17	$ (97)	$ 25

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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