Pension Benefit Obligations - Target Allocation and Plan Assets (Details)	Sep. 30, 2019	Sep. 30, 2018
United States
Components of net periodic benefit cost:
Target allocations (as a percent)	100.00%
Plan assets (as a percent)	100.00%	100.00%
United States | Equity securities
Components of net periodic benefit cost:
Target allocations (as a percent)	45.00%
Plan assets (as a percent)	45.00%	40.00%
United States | Debt
Components of net periodic benefit cost:
Target allocations (as a percent)	42.00%
Plan assets (as a percent)	45.00%	50.00%
United States | Cash and cash equivalents
Components of net periodic benefit cost:
Target allocations (as a percent)	3.00%
Plan assets (as a percent)	1.00%	1.00%
United States | Property And Other
Components of net periodic benefit cost:
Target allocations (as a percent)	10.00%
Plan assets (as a percent)	9.00%	9.00%
International
Components of net periodic benefit cost:
Target allocations (as a percent)	100.00%
Plan assets (as a percent)	100.00%	100.00%
International | Equity securities
Components of net periodic benefit cost:
Target allocations (as a percent)	37.00%
Plan assets (as a percent)	36.00%	38.00%
International | Debt
Components of net periodic benefit cost:
Target allocations (as a percent)	36.00%
Plan assets (as a percent)	31.00%	36.00%
International | Cash and cash equivalents
Components of net periodic benefit cost:
Target allocations (as a percent)	6.00%
Plan assets (as a percent)	3.00%	7.00%
International | Property And Other
Components of net periodic benefit cost:
Target allocations (as a percent)	21.00%
Plan assets (as a percent)	30.00%	19.00%