AOCI (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amounts reclassified from AOCI:
OCI	$ (248)	$ (88)	$ (104)
Pension and OPEB Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,004)	(764)	(723)
OCI before reclassifications, net of tax	(217)	(129)	(91)
Amounts reclassified from AOCI:
OCI	(160)	(84)	(41)
Reclassification of certain tax effects		(156)
AOCI, ending balance	(1,164)	(1,004)	(764)
Pension and OPEB Costs \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	75	72	80
Tax effect	18	27	30
Amounts reclassified, net of tax	57	45	50
Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(92)	(92)	(83)
OCI before reclassifications, net of tax	52	7	(16)
Amounts reclassified from AOCI:
OCI	61	18	(9)
Reclassification of certain tax effects		(18)
AOCI, ending balance	(31)	(92)	(92)
Cash Flow Hedges \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	12	15	11
Tax effect	3	4	4
Amounts reclassified, net of tax	9	11	7
AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(356)	(259)	(34)
OCI before reclassifications, net of tax	(159)	(23)	(201)
Amounts reclassified from AOCI:
OCI	(144)	(27)	(225)
Reclassification of certain tax effects		(70)
AOCI, ending balance	(500)	(356)	(259)
AFS Securities \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	20	(7)	(39)
Tax effect	5	(3)	(15)
Amounts reclassified, net of tax	15	(4)	(24)
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(15)	(17)	(188)
OCI before reclassifications, net of tax	(6)	5	149
Amounts reclassified from AOCI:
OCI	(5)	5	171
Reclassification of certain tax effects		(3)
AOCI, ending balance	(20)	(15)	(17)
Other, net \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	1	0	34
Tax effect	0	0	12
Amounts reclassified, net of tax	1	0	22
Total
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,467)	(1,132)	(1,028)
OCI before reclassifications, net of tax	(330)	(140)	(159)
Amounts reclassified from AOCI:
OCI	(248)	(88)	(104)
Reclassification of certain tax effects		(247)
AOCI, ending balance	(1,715)	(1,467)	(1,132)
Total \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	108	80	86
Tax effect	26	28	31
Amounts reclassified, net of tax	$ 82	$ 52	$ 55

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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