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Benefit Plans Fair Value Measurements (Details) $ in Millions		12 Months Ended
		Sep. 30, 2019 USD ($) Years	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Defined Benefit Plan Disclosure
Fair value of gross plan assets		$ 8,472	$ 8,531
Estimated future decommissioning cost	[1]	5,616	4,779	$ 4,304
Derivative liabilities		136	115
Net payables		132	95
Payables for collateral on loaned securities		$ 224	318
Voting percentage required to desolve partnership in private equity		80.00%
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		$ 2,670	2,644
Derivative liabilities		4	3
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2,800	2,774
Derivative liabilities		132	112
Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		58	88
Estimated future decommissioning cost		42	58
Derivative liabilities		0	0
Equity securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,766	1,787
Equity securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,762	1,786
Equity securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Equity securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		4	1
Preferred securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		10	10
Preferred securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1	4
Preferred securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		9	6
Preferred securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Corporate debt securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,387	1,151
Corporate debt securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Corporate debt securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,382	1,148
Corporate debt securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		5	3
Residential mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		427	377
Residential mortgage-backed securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Residential mortgage-backed securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		424	371
Residential mortgage-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	6
Debt securities issued by U.S. Treasury and other U.S. government agencies
Defined Benefit Plan Disclosure
Fair value of gross plan assets		807	696
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		807	696
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Asset-backed securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		144	129
Asset-backed securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Asset-backed securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		116	103
Asset-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		28	26
Debt securities issued by state/local governments
Defined Benefit Plan Disclosure
Fair value of gross plan assets		18	17
Debt securities issued by state/local governments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt securities issued by state/local governments | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		18	17
Debt securities issued by state/local governments | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt securities issued by foreign governments
Defined Benefit Plan Disclosure
Fair value of gross plan assets		210	322
Debt securities issued by foreign governments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt securities issued by foreign governments | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		209	304
Debt securities issued by foreign governments | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1	18
Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		81	74
Commercial mortgage-backed securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Commercial mortgage-backed securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		80	70
Commercial mortgage-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1	4
Equity security commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		795	1,175
Equity security commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Equity security commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Equity security commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt security commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		308	317
Debt security commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt security commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Debt security commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Commodity commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		217	232
Commodity commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Commodity commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Commodity commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Blended security commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		125	109
Blended security commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Blended security commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Blended security commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Institutional mutual funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		97	109
Institutional mutual funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		97	109
Institutional mutual funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Institutional mutual funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Cash equivalents and other short-term investments
Defined Benefit Plan Disclosure
Fair value of gross plan assets		329	466
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1	42
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		328	424
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Certificates of deposit
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	2
Certificates of deposit | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Certificates of deposit | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	2
Certificates of deposit | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private Credit [Member]
Defined Benefit Plan Disclosure
Fair value of gross plan assets		78	8
Private Credit [Member] | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private Credit [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private Credit [Member] | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private equity funds measured at net asset value
Defined Benefit Plan Disclosure
Fair value of gross plan assets		891	631
Private equity funds measured at net asset value | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private equity funds measured at net asset value | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private equity funds measured at net asset value | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private real estate funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		546	583
Private real estate funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private real estate funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Private real estate funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Securities lending commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		224	318
Securities lending commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Securities lending commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		224	318
Securities lending commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Futures
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2	7
Derivative liabilities		4	3
Futures | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2	7
Derivative liabilities		4	3
Futures | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Derivative liabilities		0	0
Futures | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Derivative liabilities		0	0
Purchased options
Defined Benefit Plan Disclosure
Fair value of gross plan assets		5
Purchased options | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0
Purchased options | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		5
Purchased options | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0
Interest Rate Swap
Defined Benefit Plan Disclosure
Derivative liabilities		12
Interest Rate Swap | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Derivative liabilities		0
Interest Rate Swap | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Derivative liabilities		12
Interest Rate Swap | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Derivative liabilities		0
Foreign currency forward
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1	3
Derivative liabilities		1	3
Foreign currency forward | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Derivative liabilities		0	0
Foreign currency forward | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1	3
Derivative liabilities		1	3
Foreign currency forward | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	0
Derivative liabilities		0	0
Written options
Defined Benefit Plan Disclosure
Fair value of gross plan assets			8
Written options | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Written options | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets			8
Written options | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Credit default swaps
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1
Derivative liabilities		1	1
Credit default swaps | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0
Derivative liabilities		0	0
Credit default swaps | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1
Derivative liabilities		1	1
Credit default swaps | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0
Derivative liabilities		0	0
Securities Sold under Agreements to Repurchase [Member]
Defined Benefit Plan Disclosure
Derivative liabilities		118	108
Securities Sold under Agreements to Repurchase [Member] | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Derivative liabilities		0	0
Securities Sold under Agreements to Repurchase [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Derivative liabilities		118	108
Securities Sold under Agreements to Repurchase [Member] | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Derivative liabilities		$ 0	$ 0
Minimum
Defined Benefit Plan Disclosure
Number of years partnerships in private equity generally continue | Years		10
Number of one year extensions for partnerships in private equity | Years		2
Maximum
Defined Benefit Plan Disclosure
Number of years partnerships in private equity generally continue | Years		12
Number of one year extensions for partnerships in private equity | Years		3
[1] (1) The current portions of the ARO liability in the amounts of $163 million and $115 million at September 30, 2019 and 2018, respectively, are included in Accounts payable and accrued liabilities.

X

- Definition

Fair value of liabilities as of the measurement date resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements. These liabilities have been segregated and restricted (usually in a trust) for the purpose of defined benefit plan benefits.

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- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. This amount is not reduced by non-benefit liabilities.

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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