Employee Benefit Plans - Components of Expense/(Income) Related to Net Benefit Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	$ 8	$ 8	$ 24	$ 28
Interest Cost	23	23	69	69
Expected Return on Plan Assets	(44)	(43)	(131)	(128)
Amortization of Net Loss	10	10	30	31
Total Income Included in Other Income - Net	(11)	(10)	(32)	(28)
Net Periodic Benefit Cost	(3)	(2)	(8)	0
Restructuring Charges - Non Operating	0	0	0	57
Total (Income) Expense	(3)	(2)	(8)	57
Other Post-retirement Benefits
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	0	0	1	1
Interest Cost	2	2	5	6
Total Income Included in Other Income - Net	2	2	5	6
Net Periodic Benefit Cost	2	2	6	7
Restructuring Charges - Non Operating	0	0	0	13
Total (Income) Expense	$ 2	$ 2	$ 6	$ 20