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Benefit Plans Fair Value Measurements (Details) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2018 USD ($) Years | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($)
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | $ 8,423 | $ 8,536 |
Estimated future decommissioning cost | [1] | 4,779 | 4,304 | $ 4,052
Derivative liabilities |  | 7 | 10 |
Net payables |  | 168 | 95 |
Payables for collateral on loaned securities |  | $ 318 | 369 |
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 |  | $ 2,644 | 2,139 |
Derivative liabilities |  | 3 | 2 |
Fair Value, Inputs, Level 2 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 2,666 | 3,207 |
Derivative liabilities |  | 4 | 6 |
Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 88 | 97 |
Estimated future decommissioning cost |  | 58 | 90 |
Derivative liabilities |  | 0 | 2 |
Equity securities |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 1,787 | 1,771 |
Equity securities | Fair Value, Inputs, Level 1 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 1,786 | 1,770 |
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 |  | 1 | 1 |
Preferred securities |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 10 | 14 |
Preferred securities | Fair Value, Inputs, Level 1 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 4 | 3 |
Preferred securities | Fair Value, Inputs, Level 2 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 6 | 11 |
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 |  | 1,151 | 1,100 |
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 |  | 1,148 | 1,088 |
Corporate debt securities | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 3 | 12 |
Residential mortgage-backed securities |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 377 | 325 |
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 |  | 371 | 317 |
Residential mortgage-backed securities | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 6 | 8 |
Debt securities issued by U.S. Treasury and other U.S. government agencies |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 696 | 193 |
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 |  | 696 | 193 |
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 |  | 129 | 146 |
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 |  | 103 | 109 |
Asset-backed securities | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 26 | 37 |
Debt securities issued by state/local governments |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 17 | 19 |
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 |  | 17 | 17 |
Debt securities issued by state/local governments | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 0 | 2 |
Debt securities issued by foreign governments |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 322 | 331 |
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 |  | 304 | 307 |
Debt securities issued by foreign governments | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 18 | 24 |
Commercial mortgage-backed securities |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 74 | 68 |
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 |  | 70 | 62 |
Commercial mortgage-backed securities | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 4 | 6 |
Equity security commingled funds |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 1,175 | 1,134 |
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 |  | 317 | 709 |
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 |  | 232 | 224 |
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 |  | 109 |  |
Blended security commingled funds | Fair Value, Inputs, Level 1 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 0 |  |
Blended security commingled funds | Fair Value, Inputs, Level 2 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 0 |  |
Blended security commingled funds | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 0 |  |
Institutional mutual funds |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 109 | 155 |
Institutional mutual funds | Fair Value, Inputs, Level 1 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 109 | 155 |
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 |  | 358 | 916 |
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 1 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 42 | 0 |
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 2 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 316 | 916 |
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 |  | 2 | 6 |
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 |  | 2 | 6 |
Certificates of deposit | 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 |  | 631 | 500 |
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 |  | 583 | 533 |
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 |  | 318 | 369 |
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 |  | 318 | 369 |
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 |  | 7 |  |
Derivative liabilities |  | 3 | 3 |
Futures | Fair Value, Inputs, Level 1 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 7 |  |
Derivative liabilities |  | 3 | 2 |
Futures | Fair Value, Inputs, Level 2 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 0 |  |
Derivative liabilities |  | 0 | 0 |
Futures | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 0 |  |
Derivative liabilities |  | 0 | 1 |
Purchased options |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 8 |  |
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 |  | 8 |  |
Purchased options | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 0 |  |
Foreign currency forward |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Fair value of gross plan assets |  | 3 | 4 |
Derivative liabilities |  | 3 | 6 |
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 |  | 3 | 4 |
Derivative liabilities |  | 3 | 6 |
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 |  |  | 1 |
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 |  |  | 1 |
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 |  |  |  |
Derivative liabilities |  | 1 | 1 |
Credit default swaps | Fair Value, Inputs, Level 1 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Derivative liabilities |  | 0 | 0 |
Credit default swaps | Fair Value, Inputs, Level 2 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Derivative liabilities |  | 1 | 0 |
Credit default swaps | Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Derivative liabilities |  | $ 0 | $ 1 |
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 $115 million and $128 million as of September 30, 2018 and 2017, 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. + References No definition available. + Details
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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. + References No definition available. + Details
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