Employee Benefit Plans (Quarterly Info) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	$ 8	$ 11	$ 23	$ 33
Interest cost	9	13	28	38
Expected return on plan assets	(13)	(15)	(40)	(46)
Amortization of net actuarial loss	5	3	16	11
Net actuarial loss from settlements	1	1	9	1
Net periodic benefit cost (credit)	10	13	36	37
Employer contributions			12
Estimated future employer contributions in current fiscal year	2		2
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	1	1	1	1
Interest cost	2	2	5	6
Expected return on plan assets	(3)	(3)	(8)	(8)
Reclassification to regulatory liability	0	0	1	1
Net periodic benefit cost (credit)	0	$ 0	(1)	$ 0
Employer contributions			4
Estimated future employer contributions in current fiscal year	$ 1		$ 1