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Benefit Plans Obligations and Funded Status (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2015 | Sep. 30, 2014 | Sep. 30, 2013
Defined Benefit Plan, Funded Status of Plan [Abstract] |  |  |  |
Amount of defined benefit plan actuarial gain (loss) from change in COLA |  | $ 232 |  |
Pension Benefits |  |  |  |
Change in benefit obligation |  |  |  |
Benefit obligation |  | 12,824 | $ 12,265 | $ 11,471
Service cost |  | 130 | 130 | 154
Interest cost |  | 540 | 558 | 468
Plan participants' contributions |  | 25 | 28 |
Amendments |  | 0 | 2 |
Actuarial loss (gain) |  | 556 | 722 |
Net transfers from variable fund/401(k) plan |  | 11 | 13 |
Expenses paid |  | (6) | (6) |
Benefits paid |  | (697) | (653) |
Amount of defined benefit plan actuarial gain (loss) from change in mortality assumption |  | 518 |  |
Change in plan assets |  |  |  |
Fair value of net plan assets |  | 6,797 | 7,507 | $ 7,221
Actual return on plan assets |  | (325) | 648 |
Employer contributions | [1] | 282 | 256 |
Defined Benefit Plan, Funded Status of Plan [Abstract] |  |  |  |
Funded status |  | $ (6,027) | $ (4,758) |
Discount rate |  | 4.50% | 4.45% | 5.00%
Amount of defined benefit plan actuarial gain (loss) from discount rate change |  | $ 79 | $ (729) |
Amount of defined benefit plan actuarial gain (loss) from reduction in workforce |  | (36) |  |
Amount of defined benefit plan actuarial gain (loss) from plan demographic experience changes |  | 349 |  |
Amount of defined benefit plan actuarial gain (loss) from retirement rate assumption change |  | 88 |  |
Other Post-retirement Benefits |  |  |  |
Change in benefit obligation |  |  |  |
Benefit obligation |  | 657 | 652 | $ 656
Service cost |  | 16 | 18 | 24
Interest cost |  | 29 | 32 | 31
Collections | [2] | 94 | 93 |
Amendments |  | 0 | 0 |
Actuarial loss (gain) |  | 3 | (21) |
Net transfers from variable fund/401(k) plan |  | 0 | 0 |
Expenses paid |  | 0 | 0 |
Benefits paid |  | (137) | (126) |
Amount of defined benefit plan actuarial gain (loss) from change in mortality assumption |  | 21 |  |
Change in plan assets |  |  |  |
Fair value of net plan assets |  | 0 | 0 | $ 0
Actual return on plan assets |  | 0 | 0 |
Employer contributions | [1] | 43 | 33 |
Defined Benefit Plan, Funded Status of Plan [Abstract] |  |  |  |
Funded status |  | $ (657) | $ (652) |
Discount rate |  | 4.65% | 4.50% | 5.05%
Amount of defined benefit plan actuarial gain (loss) from discount rate change |  | $ 13 | $ 43 |
Amount of defined benefit plan actuarial gain (loss) from reduction in workforce |  |  | (17) |
Amount of defined benefit plan actuarial gain (loss) from plan demographic experience changes |  | 20 | (64) |
Amount of defined benefit plan actuarial gain (loss) from updated capita claims costs and retiree contributions |  | $ 30 |  |
Amount of defined benefit plan actuarial gain (loss) from retirement rate assumption change |  |  | $ 16 |
[1] | Other Post-Retirement Benefits Employer contributions are reduced by federal reinsurance payments and provider discounts and rebates.
[2] | Collections include retiree contributions as well as federal reinsurance payments and provider discounts and rebates.

X
- Definition Amount of gain (loss) from changes in actuarial assumptions related to discount rates which affects the defined benefit plan obligations. + References No definition available. + Details
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- Definition Amount of defined benefit plan actuarial gain (loss) from change in COLA. + References No definition available. + Details
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- Definition Amount of gain (loss) from changes in actuarial assumptions related to mortality changes which affects the defined benefit plan obligations. + References No definition available. + Details
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- Definition Amount of gain (loss) from changes in actuarial assumptions related to demographic experience changes which affects the defined benefit plan obligations. Demographic experience changes relate to to per capita costs, contributions, participation rates, and changes in plan provisions. + References No definition available. + Details
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- Definition Amount of defined benefit plan actuarial gain (loss) from reduction in workforce. + References No definition available. + Details
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- Definition Amount of defined benefit plan actuarial gain (loss) from retirement rate assumption change + References No definition available. + Details
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- Definition Amount of defined benefit plan actuarial gain (loss) from updated capita claims costs and retiree contributions + References No definition available. + Details
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- Definition The amount of contributions made by plan participants, federal reinsurance payments, and provider discounts and rebates. This item represents a periodic increase to the plan obligation and an increase to plan assets. + References No definition available. + Details
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- Definition The net transfers from employee variable funds or 401 (k) plans to pension and postretirement benefit plans. + References No definition available. + Details
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- Definition The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost) -URI http://asc.fasb.org/extlink&oid=6504192 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost) -URI http://asc.fasb.org/extlink&oid=6504226 + Details
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- Definition Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Gain or Loss -URI http://asc.fasb.org/extlink&oid=49168827 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition Amount of plan administration expenses deducted from total plan assets. + References No definition available. + Details
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- Definition The interest rate used to adjust for the time value of money for the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition 1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Projected Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6522206 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Postretirement Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503904 + Details
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- Definition The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Benefits -URI http://asc.fasb.org/extlink&oid=49170737 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Postretirement Benefits -URI http://asc.fasb.org/extlink&oid=6521376 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(5) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition The increase in the fair value of plan assets from contributions made by the employer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition The amount of contributions made by plan participants. This item represents a periodic increase to the plan obligation and an increase to plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(4) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + 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. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=49178875&loc=d3e12355-114930 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919 + Details
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- Definition The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition The amount of increase or decrease due to a change in the terms of an existing plan or the initiation of a new plan. A plan amendment may increase or decrease benefits, including those attributed to years of service already rendered. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Plan Amendment -URI http://asc.fasb.org/extlink&oid=49173939 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(7) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Service Cost (Component of Net Periodic Pension Cost) -URI http://asc.fasb.org/extlink&oid=6525008 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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