Stock-Based Compensation (Expense and Tax Benefit Information) (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense for stock option and incentive shares plans	$ 110	$ 120	$ 216
Income tax benefits recognized in income statement for compensation arrangements	18	20	42
Unrecognized compensation cost related to non-vested awards granted	$ 127
Unrecognized compensation cost is expected to be recognized, weighted-average period, years	1 year 8 months 12 days
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense for stock option and incentive shares plans	$ 98	96	192
Restricted stock and restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense for stock option and incentive shares plans	11	21	17
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense for stock option and incentive shares plans	$ 1	$ 3	$ 7

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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