Employee Benefit Plans (Quarterly Info) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost		$ 13	$ 13	$ 38	$ 40
Interest cost		15	16	44	47
Expected return on plan assets		(21)	(22)	(62)	(64)
Amortization of net actuarial loss		6	8	20	23
Net actuarial loss from settlements		0	0	0	1
Net periodic benefit cost (credit)		13	15	40	47
Employer contributions				83
Estimated future employer contributions in current fiscal year		1		1
Pension Benefits [Member] | Subsequent Event [Member] | Minimum [Member]
Components of net periodic benefit cost (credit):
Net actuarial loss from settlements	$ 70
Pension Benefits [Member] | Subsequent Event [Member] | Maximum [Member]
Components of net periodic benefit cost (credit):
Net actuarial loss from settlements	$ 100
Other Postretirement Benefits [Member]
Components of net periodic benefit cost (credit):
Service cost		0	0	1	1
Interest cost		2	2	6	6
Expected return on plan assets		(3)	(3)	(9)	(9)
Amortization of prior service cost (credit)		(3)	(3)	(10)	(11)
Reclassification to regulatory liability		1	1	3	3
Net periodic benefit cost (credit)		(3)	(3)	(9)	(10)
Amortization of prior service cost (credit) from regulatory assets (liabilities)		(2)	$ (2)	(6)	$ (7)
Employer contributions				4
Estimated future employer contributions in current fiscal year		$ 1		$ 1