Employee Benefit Plans - Components of Expense/(Income) Related to Net Benefit Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Components of expense/ (income) related to net benefit expense:
Restructuring Charges - Non Operating (a)	$ 0
Pension Benefits
Components of expense/ (income) related to net benefit expense:
Service Cost Included in Labor and Fringe	9	$ 11
Interest Cost	23	23
Expected Return on Plan Assets	(44)	(42)
Amortization of Net Loss	10	11
Total Income Included in Other Income - Net	(11)	(8)
Net Periodic Benefit Cost	(2)	3
Restructuring Charges - Non Operating (a)	0	50
Total (Income) Expense	(2)	53
Other Post-retirement Benefits
Components of expense/ (income) related to net benefit expense:
Interest Cost	2	2
Amortization of Net Loss	0	0
Net Periodic Benefit Cost	2	2
Restructuring Charges - Non Operating (a)		13
Total (Income) Expense	$ 2	$ 15