Pension and Other Employee Benefits (Pension Contributions) (Details) - USD ($)	3 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and PRB Plans [Line Items]
Required pension contributions		$ 343,000,000	$ 889,000,000	$ 615,000,000
Discretionary pension contributions	$ 1,250,000,000	0	1,250,000,000	1,000,000,000
PRB contributions		37,000,000	22,000,000	27,000,000
Payment for Pension and Other Postretirement Benefits		$ 380,000,000	$ 2,161,000,000	$ 1,642,000,000

The discretionary amount of cash and cash equivalents contributed by the entity to fund its pension plans.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount of cash outflow for other postretirement benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes pension benefit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3536-108585

+ Details

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- Definition

Amount of cash outflow for pension and other postretirement benefits. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree.

+ References

+ Details

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- Definition

Amount of cash outflow for pension benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes other postretirement benefit.

+ References

+ Details

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