Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits Cost
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	$ 10	$ 8	$ 20	$ 16
Interest Cost	21	26	41	52
Expected Return on Plan Assets	(44)	(43)	(87)	(86)
Amortization of Net Loss	14	8	28	15
Total Included in Other Income - Net	(9)	(9)	(18)	(19)
Net Periodic Benefit Cost/(Credit)	1	(1)	2	(3)
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	0	1	1	2
Amortization of Prior Service Costs	(1)	(1)	(3)	(3)
Total Included in Other Income - Net	(1)	0	(2)	(1)
Net Periodic Benefit Cost/(Credit)	$ 0	$ 1	$ (1)	$ 0