Employee Benefit Plans (Quarterly Info) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	$ 7	$ 7	$ 15	$ 15
Interest cost	7	9	14	19
Expected return on plan assets	(11)	(14)	(22)	(27)
Amortization of net actuarial loss	3	7	7	11
Net actuarial loss from settlements	1	2	1	8
Net periodic benefit cost (credit)	7	11	15	26
Employer contributions			3
Estimated future employer contributions in current fiscal year	1		1
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (credit):
Interest cost	2	1	3	3
Expected return on plan assets	(3)	(2)	(5)	(5)
Reclassification to regulatory liability	0	0	1	1
Net periodic benefit cost (credit)	(1)	$ (1)	(1)	$ (1)
Employer contributions			3
Estimated future employer contributions in current fiscal year	$ 2		$ 2