Employee Benefit Plans - Components of Expense/(Income) Related to Net Benefit Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	$ 7	$ 9	$ 16	$ 20
Interest Cost	23	23	46	46
Expected Return on Plan Assets	(43)	(43)	(87)	(85)
Amortization of Net Loss	10	10	20	21
Total Income Included in Other Income - Net	(10)	(10)	(21)	(18)
Net Periodic Benefit Cost	(3)	(1)	(5)	2
Restructuring Charges - Non Operating	0	7	0	57
Total (Income) Expense	(3)	6	(5)	59
Other Post-retirement Benefits
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	1	1	1	1
Interest Cost	1	2	3	4
Total Income Included in Other Income - Net	1	2	3	4
Net Periodic Benefit Cost	2	3	4	5
Restructuring Charges - Non Operating	0	0	0	13
Total (Income) Expense	$ 2	$ 3	$ 4	$ 18