Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits Cost
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	$ 8	$ 7	$ 16	$ 16
Interest Cost	26	23	52	46
Expected Return on Plan Assets	(43)	(43)	(86)	(87)
Amortization of Net Loss	8	10	15	20
Total Included in Other Income - Net	(9)	(10)	(19)	(21)
Net Periodic Benefit Cost	(1)	(3)	(3)	(5)
Other Post-retirement Benefits Cost
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	1	1	1	1
Interest Cost	1	1	2	3
Amortization of Prior Service Costs	(1)	0	(3)	0
Total Included in Other Income - Net	0	1	(1)	3
Net Periodic Benefit Cost	$ 1	$ 2	$ 0	$ 4