Employee Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	$ 4	$ 4	$ 13	$ 13
Interest costs	10	12	30	35
Expected return on plan assets	0	0	0	0
Amortization of net actuarial (gains) losses	10	6	30	20
Amortization of prior service costs (credit)	(1)	(1)	(2)	(2)
Allocated to affiliates	18	15	56	49
Net periodic benefit costs (credit)	18	15	56	49
Pension Benefits | Affiliated Entity
Net periodic benefit costs [Abstract]
Allocated to affiliates	(5)	(6)	(15)	(17)
Net periodic benefit costs (credit)	(5)	(6)	(15)	(17)
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	0	0	0	0
Interest costs	0	1	0	1
Expected return on plan assets	0	(1)	0	(1)
Amortization of net actuarial (gains) losses	0	0	0	0
Amortization of prior service costs (credit)	0	0	0	0
Allocated to affiliates	0	0	0	0
Net periodic benefit costs (credit)	0	0	0	0
Other Postretirement Benefits | Affiliated Entity
Net periodic benefit costs [Abstract]
Allocated to affiliates	0	0	0	0
Net periodic benefit costs (credit)	$ 0	$ 0	$ 0	$ 0