EBP Net Periodic Benefit Cost & OCI (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	$ 31	$ 45	$ 50
Interest cost	36	50	46
Expected return on plan assets	(53)	(61)	(63)
Amortization of prior service credit	0	0	0
Amortization of net actuarial loss	21	15	23
Net actuarial loss from settlements	9	1	23
Reclassification to regulatory liability	0	0	0
Net periodic benefit cost (credit)	44	50	79
Other changes in plan assets and benefit obligations recognized in Other comprehensive income (loss):
Net actuarial gain (loss)	112	88	(18)
Amortization of net actuarial loss	21	15	23
Net actuarial loss from settlements	9	1	23
Other changes in plan assets and benefit obligations recognized in Other comprehensive income (loss)	142	104	28
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	1	1	1
Interest cost	7	8	7
Expected return on plan assets	(11)	(10)	(11)
Amortization of prior service credit	0	0	(2)
Amortization of net actuarial loss	0	0	0
Net actuarial loss from settlements	0	0	0
Reclassification to regulatory liability	2	1	2
Net periodic benefit cost (credit)	(1)	0	(3)
Other changes in plan assets and benefit obligations recognized in Other comprehensive income (loss):
Net actuarial gain (loss)	(4)	(9)	9
Amortization of net actuarial loss	0	0	0
Net actuarial loss from settlements	0	0	0
Other changes in plan assets and benefit obligations recognized in Other comprehensive income (loss)	(4)	(9)	9
Other changes in plan assets and benefit obligations recognized in regulatory (assets) and liabilities:
Net actuarial gain (loss)	21	7	(10)
Amortization of prior service credit	$ 0	$ 0	(2)
Other Nonoperating Income (Expense) [Member] | Pension Benefits [Member]
Components of net periodic benefit cost (credit):
Net actuarial loss from settlements			$ 23