Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Benefits [Member]
Components of Net Periodic (Benefit) Cost [Abstract]
Service cost	$ 1		$ 2	$ 2
Interest cost	17	$ 24	53	70
Expected return on plan assets	(41)	(43)	(127)	(130)
Amortization of unrecognized net loss	12	12	37	35
Amortization of unrecognized prior service cost				1
Settlement charge		1	2	8
Regulatory asset decrease	1		1
Net periodic (benefit) cost	(10)	(6)	(32)	(14)
Other Postretirement Benefits [Member]
Components of Net Periodic (Benefit) Cost [Abstract]
Net periodic (benefit) cost	$ (1)	$ 0	$ (1)	$ (1)