Revenue Unpaid Incentives (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Paid Economic Incentives	$ 76	$ 70	$ 231	$ 206
Unpaid Economic Incentives	$ 154		$ 154		$ 145

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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