AOCI (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amounts reclassified from AOCI:
OCI	$ 871	$ (248)	$ (88)
Pension and OPEB Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,164)	(1,004)	(764)
OCI before reclassifications, net of tax	(42)	(217)	(129)
Amounts reclassified from AOCI:
OCI	42	(160)	(84)
Reclassification of certain tax effects			(156)
AOCI, ending balance	(1,122)	(1,164)	(1,004)
Pension and OPEB Costs \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	111	75	72
Tax effect	27	18	27
Amounts reclassified, net of tax	84	57	45
Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(31)	(92)	(92)
OCI before reclassifications, net of tax	(89)	52	7
Amounts reclassified from AOCI:
OCI	(70)	61	18
Reclassification of certain tax effects			(18)
AOCI, ending balance	(101)	(31)	(92)
Cash Flow Hedges \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	25	12	15
Tax effect	6	3	4
Amounts reclassified, net of tax	19	9	11
AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(500)	(356)	(259)
OCI before reclassifications, net of tax	790	(159)	(23)
Amounts reclassified from AOCI:
OCI	880	(144)	(27)
Reclassification of certain tax effects			(70)
AOCI, ending balance	380	(500)	(356)
AFS Securities \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	119	20	(7)
Tax effect	29	5	(3)
Amounts reclassified, net of tax	90	15	(4)
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(20)	(15)	(17)
OCI before reclassifications, net of tax	18	(6)	5
Amounts reclassified from AOCI:
OCI	19	(5)	5
Reclassification of certain tax effects			(3)
AOCI, ending balance	(1)	(20)	(15)
Other, net \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	1	1	0
Tax effect	0	0	0
Amounts reclassified, net of tax	1	1	0
Total
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,715)	(1,467)	(1,132)
OCI before reclassifications, net of tax	677	(330)	(140)
Amounts reclassified from AOCI:
OCI	871	(248)	(88)
Reclassification of certain tax effects			(247)
AOCI, ending balance	(844)	(1,715)	(1,467)
Total \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	256	108	80
Tax effect	62	26	28
Amounts reclassified, net of tax	$ 194	$ 82	$ 52

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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Represents the quantification of the effect of adopting the new accounting standard or change in accounting principle expected by the entity to have a significant effect on the entity's financial statements.

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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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Amount before tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated 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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