Acquisitions - Schedule of Preliminary Purchase Price Allocation (Details) - USD ($) $ in Millions |
Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2017 |
|---|---|---|---|
| Business Acquisition [Line Items] | |||
| Goodwill | $ 15,656 | $ 15,194 | $ 15,110 |
| 2019 Business Acquisitions | |||
| Business Acquisition [Line Items] | |||
| Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Tangible Assets | 25 | ||
| Intangible assets | 319 | ||
| Goodwill | 643 | ||
| Fair value of net assets acquired | 987 | ||
| Fair value of previously-held interest in the acquired entities | $ 47 |