Benefit Plans Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other Pension Plan
Retirement Plan Disclosure
Defined benefit plan contributions			$ 225
Pension Benefits
Retirement Plan Disclosure
Service cost	$ 14	$ 11	41	$ 33
Interest cost	104	125	312	374
Expected return on plan assets	122	(119)	366	(358)
Amortization of prior service cost	(25)	(25)	(73)	(74)
Recognized net actuarial loss	(109)	84	(327)	252
Total net periodic benefit cost as actuarially determined	80	76	241	227
Amount capitalized due to actions of regulator	(3)	0	(11)	(1)
Total net periodic benefit cost	77	76	230	228
Other Post-retirement Benefits
Retirement Plan Disclosure
Defined benefit plan contributions			19
Service cost	4	2	12	8
Interest cost	4	5	12	14
Expected return on plan assets	0		0	0
Amortization of prior service cost	(6)	(6)	(18)	(18)
Recognized net actuarial loss	(2)	1	(7)	3
Total net periodic benefit cost as actuarially determined	4	2	13	7
Amount capitalized due to actions of regulator	0		0	0
Total net periodic benefit cost	$ 4	$ 2	$ 13	$ 7