Goodwill - Narrative (Details) $ in Millions |
2 Months Ended | 3 Months Ended | 10 Months Ended | 12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
Jul. 01, 2016
USD ($)
|
Dec. 15, 2017
USD ($)
|
Jun. 30, 2017
USD ($)
|
Sep. 30, 2018
USD ($)
|
Sep. 30, 2018
USD ($)
|
Sep. 30, 2018
USD ($)
reporting_unit
|
Sep. 30, 2017
USD ($)
|
Sep. 30, 2016
USD ($)
|
Jul. 31, 2018 |
Jul. 01, 2018
USD ($)
|
Dec. 16, 2017
USD ($)
|
|
| Goodwill [Line Items] | |||||||||||
| Goodwill | $ 2,658 | $ 2,764 | $ 2,764 | $ 2,764 | $ 3,542 | $ 2,658 | |||||
| Number of reporting units | 5 | 5 | |||||||||
| Impairment loss | $ 0 | 52 | $ 442 | ||||||||
| Unified Communications Solutions Provider | |||||||||||
| Goodwill [Line Items] | |||||||||||
| Goodwill | $ 946 | ||||||||||
| Impairment loss | 442 | ||||||||||
| Goodwill, fair value | $ 504 | ||||||||||
| Predecessor | |||||||||||
| Goodwill [Line Items] | |||||||||||
| Goodwill | 2,658 | 3,542 | 3,629 | ||||||||
| Impairment loss | $ 0 | $ 52 | $ 52 | $ 442 | |||||||
| Professional Services | |||||||||||
| Goodwill [Line Items] | |||||||||||
| Goodwill | $ 22 | ||||||||||
| Global Support Services | |||||||||||
| Goodwill [Line Items] | |||||||||||
| Goodwill | $ 1,448 | ||||||||||
| Goodwill, measurement input | 1.10% | ||||||||||
| Fair value in excess of carrying amount, percent | 7.00% | ||||||||||