Retirement Plans - Schedule of Fair Values of Defined Benefit Plan Assets Organized by Asset Class and Fair Value Hierarchy of ASC 820 (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 4,454	$ 4,533
Percentage of defined benefit plan assets	100.00%	100.00%
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 727	$ 621
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	1,544	1,635
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	126	130
Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	2,057	2,147
U.S. equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 1,024	$ 1,044
Percentage of defined benefit plan assets	23.00%	23.00%
U.S. equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 396	$ 405
U.S. equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	9	6
U.S. equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0
U.S. equities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	619	633
International equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 327	$ 358
Percentage of defined benefit plan assets	7.00%	8.00%
International equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 210	$ 225
International equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	14	10
International equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0
International equities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	103	123
Emerging market equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 119	$ 125
Percentage of defined benefit plan assets	3.00%	3.00%
Emerging market equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 0	$ 0
Emerging market equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	1	1
Emerging market equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0
Emerging market equities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	118	124
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 1,851	$ 2,002
Percentage of defined benefit plan assets	42.00%	44.00%
Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 0	$ 0
Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	1,008	1,143
Corporate bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0
Corporate bonds | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	843	859
Government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 629	$ 620
Percentage of defined benefit plan assets	14.00%	14.00%
Government bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 0	$ 0
Government bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	505	468
Government bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0
Government bonds | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	124	152
Other
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 504	$ 384
Percentage of defined benefit plan assets	11.00%	8.00%
Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 121	$ (9)
Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	7	7
Other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	126	130
Other | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 250	$ 256