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Fair Value Measurements Fair Value Measurements - Investments (Details) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 USD ($) Units | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) Units | Jun. 30, 2020 USD ($) | Sep. 30, 2020 USD ($)
Investment Gains (Losses) |  |  |  |  |
Financing Receivable, after Allowance for Credit Loss | $ 109 |  | $ 109 |  | $ 93
Balance in NDT | $ 2,800 |  | $ 2,800 |  |
Period of time where the investor contributes capital to an investment in a private partnership - minimum | Units | 3 |  | 3 |  |
Period of time where the investor contributes capital to an investment in a private partnership - maximum | Units | 4 |  | 4 |  |
Minimum investment period | Units | 10 |  | 10 |  |
Number of readily available quoted exchange prices for the investments | 0 |  | 0 |  |
Investment funds | $ 3,968 |  | $ 3,968 |  | $ 3,198
LTDCP [Member] |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
Unrealized gains (losses) on investments | (1) | $ (2) | (1) | $ 0 |
SERP |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
Unrealized gains (losses) on investments | (3) | (7) | (8) | 1 |
ART [Member] |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
Unrealized gains (losses) on investments | (48) | (97) | (168) | 1 |
NDT [Member] |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
Unrealized gains (losses) on investments | (107) | $ (235) | 361 | $ 11 |
Equity Funds |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
NDT unfunded commitments related to private equity and real estate | 231 |  | 231 |  |
Real Estate Funds |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
NDT unfunded commitments related to private equity and real estate | 85 |  | 85 |  |
Credit [Member] |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
NDT unfunded commitments related to private equity and real estate | 42 |  | 42 |  |
Private Equity Funds [Member] |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
NDT unfunded commitments related to private equity and real estate | 135 |  | 135 |  |
Private real estate funds [Member] |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
Fair value plan assets gross | 66 |  | 66 |  |
Private Credit [Member] |  |  |  |  |
Investment Gains (Losses) |  |  |  |  |
NDT unfunded commitments related to private equity and real estate | $ 20 |  | $ 20 |  |

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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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