Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits Cost
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	$ 10	$ 8
Interest Cost	20	26
Expected Return on Plan Assets	(43)	(43)
Amortization of Net Loss	14	7
Total Included in Other Income - Net	(9)	(10)
Net Periodic Benefit Cost/(Credit)	1	(2)
Other Post-retirement Benefits Cost
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	0	0
Interest Cost	1	1
Amortization of Prior Service Costs	(2)	(2)
Total Included in Other Income - Net	(1)	(1)
Net Periodic Benefit Cost/(Credit)	$ (1)	$ (1)