Employee Benefit Plans (Quarterly Info) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	$ 7	$ 11	$ 15	$ 22
Interest cost	9	13	19	25
Expected return on plan assets	(14)	(16)	(27)	(31)
Amortization of net actuarial loss	7	4	11	8
Net actuarial loss from settlements	2	0	8	0
Net periodic benefit cost (credit)	11	12	26	24
Employer contributions			11
Estimated future employer contributions in current fiscal year	3		3
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (credit):
Interest cost	1	2	3	4
Expected return on plan assets	(2)	(3)	(5)	(5)
Reclassification to regulatory liability	0	1	1	1
Net periodic benefit cost (credit)	(1)	$ 0	(1)	$ 0
Employer contributions			3
Estimated future employer contributions in current fiscal year	$ 2		$ 2