Employee Benefit Plans (Quarterly Info) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	$ 11	$ 12	$ 33	$ 37
Interest cost	13	12	38	35
Expected return on plan assets	(15)	(16)	(46)	(47)
Amortization of net actuarial loss	3	6	11	17
Net actuarial loss from settlements	1	1	1	2
Net periodic benefit cost (credit)	13	15	37	44
Employer contributions			63
Estimated future employer contributions in current fiscal year	1		1
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost	1	1	1	1
Interest cost	2	1	6	5
Expected return on plan assets	(3)	(2)	(8)	(8)
Amortization of prior service cost (credit)	0	0	0	(1)
Reclassification to regulatory liability	0	0	1	1
Net periodic benefit cost (credit)	0	$ 0	0	(2)
Amortization of prior service cost (credit) from regulatory assets (liabilities)				$ (1)
Employer contributions			4
Estimated future employer contributions in current fiscal year	$ 1		$ 1