AOCI (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Amounts reclassified from AOCI:
OCI	$ 294	$ (178)
Pension and OPEB Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,164)	(1,004)
OCI before reclassifications, net of tax	0	0
Amounts reclassified from AOCI:
OCI	17	14
AOCI, ending balance	(1,147)	(990)
Pension and OPEB Costs \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	23	18
Tax effect	6	4
Amounts reclassified, net of tax	17	14
Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(31)	(92)
OCI before reclassifications, net of tax	(30)	70
Amounts reclassified from AOCI:
OCI	(34)	78
AOCI, ending balance	(65)	(14)
Cash Flow Hedges \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	(5)	11
Tax effect	(1)	3
Amounts reclassified, net of tax	(4)	8
AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(500)	(356)
OCI before reclassifications, net of tax	314	(282)
Amounts reclassified from AOCI:
OCI	309	(268)
AOCI, ending balance	(191)	(624)
AFS Securities \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	(6)	19
Tax effect	(1)	5
Amounts reclassified, net of tax	(5)	14
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(20)	(15)
OCI before reclassifications, net of tax	2	(2)
Amounts reclassified from AOCI:
OCI	2	(2)
AOCI, ending balance	(18)	(17)
Other, net \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	0	0
Tax effect	0	0
Amounts reclassified, net of tax	0	0
Total
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(1,715)	(1,467)
OCI before reclassifications, net of tax	286	(214)
Amounts reclassified from AOCI:
OCI	294	(178)
AOCI, ending balance	(1,421)	(1,645)
Total \| Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	12	48
Tax effect	4	12
Amounts reclassified, net of tax	$ 8	$ 36

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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