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) - Pension Plan - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 4,705	$ 4,855
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	$ 552	$ 605
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	2,092	2,149
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	143	132
Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	1,918	1,969
U.S. equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 837	$ 875
Percentage of defined benefit plan assets	18.00%	18.00%
U.S. equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 246	$ 245
U.S. equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	10	10
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	581	620
International equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 291	$ 231
Percentage of defined benefit plan assets	6.00%	5.00%
International equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 169	$ 154
International equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	11	12
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	111	65
Emerging market equities
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 95	$ 102
Percentage of defined benefit plan assets	2.00%	2.00%
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	0
Emerging market equities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	94	101
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 2,005	$ 2,100
Percentage of defined benefit plan assets	43.00%	43.00%
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	1,170	1,221
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	835	879
Government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 1,005	$ 1,012
Percentage of defined benefit plan assets	21.00%	21.00%
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	899	904
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	106	108
Other
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 472	$ 535
Percentage of defined benefit plan assets	10.00%	11.00%
Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 137	$ 206
Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	1	1
Other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	143	132
Other | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plan assets	$ 191	$ 196