AOCI (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Amounts reclassified from AOCI:
OCI	$ 302	$ (61)	$ 596	$ (239)
Pension and OPEB Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,147)	(990)	(1,164)	(1,004)
OCI before reclassifications, net of tax	0	0	0	0
Amounts reclassified from AOCI:
OCI	19	13	36	27
AOCI, ending balance	(1,128)	(977)	(1,128)	(977)
Pension and OPEB Costs \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	24	18	47	36
Tax effect	5	5	11	9
Amounts reclassified, net of tax	19	13	36	27
Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(65)	(14)	(31)	(92)
OCI before reclassifications, net of tax	(61)	23	(91)	93
Amounts reclassified from AOCI:
OCI	(59)	26	(93)	104
AOCI, ending balance	(124)	12	(124)	12
Cash Flow Hedges \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	2	3	(3)	14
Tax effect	0	0	(1)	3
Amounts reclassified, net of tax	2	3	(2)	11
AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(191)	(624)	(500)	(356)
OCI before reclassifications, net of tax	346	(100)	660	(382)
Amounts reclassified from AOCI:
OCI	342	(99)	651	(367)
AOCI, ending balance	151	(723)	151	(723)
AFS Securities \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	(6)	1	(12)	20
Tax effect	(2)	0	(3)	5
Amounts reclassified, net of tax	(4)	1	(9)	15
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(18)	(17)	(20)	(15)
OCI before reclassifications, net of tax	0	(2)	2	(4)
Amounts reclassified from AOCI:
OCI	0	(1)	2	(3)
AOCI, ending balance	(18)	(18)	(18)	(18)
Other, net \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	0	1	0	1
Tax effect	0	0	0	0
Amounts reclassified, net of tax	0	1	0	1
Total
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,421)	(1,645)	(1,715)	(1,467)
OCI before reclassifications, net of tax	285	(79)	571	(293)
Amounts reclassified from AOCI:
OCI	302	(61)	596	(239)
AOCI, ending balance	(1,119)	(1,706)	(1,119)	(1,706)
Total \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	20	23	32	71
Tax effect	3	5	7	17
Amounts reclassified, net of tax	$ 17	$ 18	$ 25	$ 54

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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