Employee Benefit Plans Employee Benefit Plans (Obligations, Funded Status, and Periodic Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	$ 10,591	$ 11,409	$ 10,741
Estimated fair value of plan assets	8,948	9,688	9,009
Over (under) funded status	(1,643)	(1,721)
Net periodic benefit costs	259	349	359
Pension Benefits | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	9,580	10,500
Estimated fair value of plan assets	8,615	9,371
Over (under) funded status	(965)	(1,129)
Net periodic benefit costs	176	267
Pension Benefits | Non- U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	1,011	909
Estimated fair value of plan assets	333	317
Over (under) funded status	(678)	(592)
Net periodic benefit costs	83	82
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	1,324	1,674	1,759
Estimated fair value of plan assets	1,360	1,434	1,386
Over (under) funded status	36	(240)
Net periodic benefit costs	(64)	(10)	$ 39
Other Postretirement Benefits | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	1,288	1,648
Estimated fair value of plan assets	1,334	1,426
Over (under) funded status	46	(222)
Net periodic benefit costs	(66)	(12)
Other Postretirement Benefits | Non- U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	36	26
Estimated fair value of plan assets	26	8
Over (under) funded status	(10)	(18)
Net periodic benefit costs	$ 2	$ 2