Employee Benefit Plans Employee Benefit Plans (Obligations, Funded Status, and Periodic Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	$ 11,409	$ 10,741	$ 10,293
Estimated fair value of plan assets	9,688	9,009	8,603
Over (under) funded status	(1,721)	(1,732)
Net periodic benefit costs	349	359	342
Pension Benefits | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	10,500	9,859
Estimated fair value of plan assets	9,371	8,721
Over (under) funded status	(1,129)	(1,138)
Net periodic benefit costs	267	278
Pension Benefits | Non- U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	909	882
Estimated fair value of plan assets	317	288
Over (under) funded status	(592)	(594)
Net periodic benefit costs	82	81
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	1,674	1,759	1,892
Estimated fair value of plan assets	1,434	1,386	1,382
Over (under) funded status	(240)	(373)
Net periodic benefit costs	(10)	39	$ 66
Other Postretirement Benefits | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	1,648	1,734
Estimated fair value of plan assets	1,426	1,379
Over (under) funded status	(222)	(355)
Net periodic benefit costs	(12)	37
Other Postretirement Benefits | Non- U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	26	25
Estimated fair value of plan assets	8	7
Over (under) funded status	(18)	(18)
Net periodic benefit costs	$ 2	$ 2