Pensions and Other Postretirement Benefits (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Net Periodic Benefit Cost, Estimated Future Employer Contributions In Current Fiscal Year	$ 140
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Net Periodic Benefit Cost, Estimated Future Employer Contributions In Current Fiscal Year	75
Service cost	14	$ 15
Interest cost	43	50
Expected return on plan assets	(69)	(70)
Amortization of actuarial losses	31	30
Amortization of prior service cost	0	(1)
Net periodic pension/other postretirement benefit cost	19	24
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Net Periodic Benefit Cost, Estimated Future Employer Contributions In Current Fiscal Year	65
Service cost	4	5
Interest cost	10	12
Expected return on plan assets	0	0
Amortization of actuarial losses	4	8
Amortization of prior service cost	(2)	(3)
Net periodic pension/other postretirement benefit cost	$ 16	$ 22