PENSION AND POSTRETIREMENT 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, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 4,855	$ 4,454
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	$ 605	$ 727
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	2,149	1,544
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	132	126
Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	1,969	2,057
U.S. equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 875	$ 1,024
Percentage of defined benefit plan assets	18.00%	23.00%
U.S. equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 245	$ 396
U.S. equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	10	9
U.S. equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0	0
U.S. equities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	620	619
International equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 231	$ 327
Percentage of defined benefit plan assets	5.00%	7.00%
International equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 154	$ 210
International equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	12	14
International equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0	0
International equities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	65	103
Emerging market equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 102	$ 119
Percentage of defined benefit plan assets	2.00%	3.00%
Emerging market equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets		$ 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	0
Emerging market equities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	101	118
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 2,100	$ 1,851
Percentage of defined benefit plan assets	43.00%	42.00%
Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets		$ 0
Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	1,221	1,008
Corporate bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0	0
Corporate bonds | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	879	843
Government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 1,012	$ 629
Percentage of defined benefit plan assets	21.00%	14.00%
Government bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets		$ 0
Government bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	904	505
Government bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	0	0
Government bonds | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	108	124
Other
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 535	$ 504
Percentage of defined benefit plan assets	11.00%	11.00%
Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 206	$ 121
Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	1	7
Other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	132	126
Other | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 196	$ 250