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Benefit Plans Fair Value Measurements (Details) $ in Millions		12 Months Ended
		Sep. 30, 2020 USD ($) Years	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Defined Benefit Plan Disclosure
Fair value of gross plan assets		$ 8,368	$ 8,472
Estimated future decommissioning cost	[1]	6,785	5,616	$ 4,779
Derivative liabilities		135	136
Net payables		107	132
Payables for collateral on loaned securities		$ 167	224
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		$ 2,679	2,670
Derivative liabilities		1	4
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2,561	2,800
Derivative liabilities		134	132
Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		42	58
Estimated future decommissioning cost		94	42
Derivative liabilities		0	0
Equity securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,624	1,766
Equity securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		1,621	1,762
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		3	4
Preferred securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		11	10
Preferred securities | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		0	1
Preferred securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		11	9
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		1,421	1,387
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		1,418	1,382
Corporate debt securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	5
Residential mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		317	427
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		314	424
Residential mortgage-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	3
Debt securities issued by U.S. Treasury and other U.S. government agencies
Defined Benefit Plan Disclosure
Fair value of gross plan assets		701	807
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		701	807
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		116	144
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		88	116
Asset-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		28	28
Debt securities issued by state/local governments
Defined Benefit Plan Disclosure
Fair value of gross plan assets		23	18
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		23	18
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		231	210
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		179	209
Debt securities issued by foreign governments | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		52	1
Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of gross plan assets		91	81
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		86	80
Commercial mortgage-backed securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets		5	1
Equity security commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		931	795
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		203	308
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
Commodity commingled funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Commodity commingled funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Commodity commingled funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Blended security commingled funds
Defined Benefit Plan Disclosure
Fair value of gross plan assets		102	125
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		277	97
Institutional mutual funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		277	97
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		338	329
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		77	1
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets		261	328
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
Certificates of deposit | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Certificates of deposit | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Fair value of gross plan assets			3
Certificates of deposit | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Fair value of gross plan assets			0
Private Credit [Member]
Defined Benefit Plan Disclosure
Fair value of gross plan assets		166	78
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		1,003	778
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		629	659
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		167	224
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		167	224
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		3	2
Derivative liabilities		1	4
Futures | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Fair value of gross plan assets		3	2
Derivative liabilities		1	4
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		10
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		10
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		6	12
Interest Rate Swap | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure
Derivative liabilities		0	0
Interest Rate Swap | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure
Derivative liabilities		6	12
Interest Rate Swap | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure
Derivative liabilities		0	0
Foreign currency forward
Defined Benefit Plan Disclosure
Fair value of gross plan assets		2	1
Derivative liabilities		3	1
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		2	1
Derivative liabilities		3	1
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			5
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			5
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		2
Derivative liabilities		2	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		2
Derivative liabilities		2	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		123	118
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		123	118
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		14
Number of one year extensions for partnerships in private equity | Years		3
[1] (1) Includes $345 million and $163 million at September 30, 2020 and 2019, respectively, in Current 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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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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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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