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Summary of Significant Accounting Policies - Pension and Postretirement Benefit Plan Amendments (Details) - Scenario, Forecast $ in Millions	3 Months Ended
	Dec. 31, 2018 USD ($)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Loss related to curtailment	$ 17
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Gain from benefit plan amendment and remeasurement	$ 2

X

- Definition

Defined Benefit Plan, Gain (Loss) From Benefit Plan Amendment And Remeasurement

+ References

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.

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- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit from event reducing expected years of future service of present employees or eliminating accrual of defined benefits for some or all future services of present employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(7)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)(7)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920

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