Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details 2) $ in Millions	3 Months Ended
Dec. 31, 2017 USD ($)
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect of change in accounting principal on operating results, retirement benefits	$ 10

Amount of the effect of a change in accounting principle on operating profit or loss.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
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-Section 50
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22580-107794

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