Employee Benefit Plans (Quarterly Info) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	$ 8	$ 11
Interest cost	10	12
Expected return on plan assets	(13)	(15)
Amortization of net actuarial loss	4	4
Net actuarial loss from settlements	6	0
Net periodic benefit cost (credit)	15	12
Estimated future employer contributions in current fiscal year	13
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (credit):
Interest cost	2	2
Expected return on plan assets	(3)	(2)
Reclassification to regulatory liability	1	0
Net periodic benefit cost (credit)	0	$ 0
Employer contributions	1
Estimated future employer contributions in current fiscal year	$ 4