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Benefit Plans Components of Benefit Plans (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Fixed and variable fund annual maximum contribution		$ 10,000
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Assets Transferred to (from) Plan		23,000,000
Defined contribution plan contribution amount	$ 88,000,000	$ 84,000,000	$ 80,000,000
Minimum
Defined Benefit Plan Disclosure
Threshold for Deferral of Actuarial Gain/Loss Under Corridor Approach		10.00%

X

- Definition

The maximum annual contribution that employees can make to the fixed and variable fund benefit. The fixed fund benefit is a benefit that earns a specified rate of interest on contributions made by employees. The variable fund is a benefit that invests employee contributions in the Spartan U.S. Equity Index Fund-Fidelity Advantage Class (Spartan).

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- Definition

Threshold for Deferral of Actuarial Gain/Loss Under Corridor Approach

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- Definition

Amount of increase (decrease) in plan assets of defined benefit plan from assets transferred into (from) plan.

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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 cost for defined contribution plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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