Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits Cost
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	$ 8	$ 8	$ 24	$ 24
Interest Cost	25	23	77	69
Expected Return on Plan Assets	(43)	(44)	(129)	(131)
Amortization of Net Loss	8	10	23	30
Total Included in Other Income - Net	(10)	(11)	(29)	(32)
Net Periodic Benefit (Credit)/Cost	(2)	(3)	(5)	(8)
Other Post-retirement Benefits Cost
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	0	0	1	1
Interest Cost	0	2	2	5
Amortization of Prior Service Costs	(2)	0	(5)	0
Total Included in Other Income - Net	(2)	2	(3)	5
Net Periodic Benefit (Credit)/Cost	$ (2)	$ 2	$ (2)	$ 6