Marketable Securities Available-for-sale Securities (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | |
|---|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2019 |
Sep. 30, 2018 |
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| Contractual maturities of available-for-sale debt securities [Abstract] | |||
| Years to maturity - less than one year | $ 51 | $ 51 | |
| Years to maturity - no single maturity date | 35 | 35 | |
| Available-for-sale debt securities, fair value | 86 | 86 | |
| Available-for-sale Securities [Abstract] | |||
| Available-for-sale debt securities, gross realized gains | $ 11 | $ 11 | |
| Available-for-sale securities equity securities, fair value | $ 167 | ||
| Available-for-sale equity securities, unrealized gains | $ 63 |
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- Definition Equity and Debt Available-for-sale Securities, Reported Amounts [Abstract] No definition available.
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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale. No definition available.
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- References No definition available.
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- Definition Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), maturing in next fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), without single maturity date and not allocated over maturity grouping. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of equity securities categorized neither as held-to-maturity nor as trading. No definition available.
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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. No definition available.
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