Employee Benefit Plans Employee Benefit Plans (Obligations, Funded Status, and Periodic Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	$ 12,873	$ 11,950	$ 10,591
Estimated fair value of plan assets	11,256	10,230	8,948
Over (under) funded status	(1,617)	(1,720)
Net periodic benefit costs	246	336	259
Pension Benefits | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	11,700	10,824
Estimated fair value of plan assets	10,692	9,742
Over (under) funded status	(1,008)	(1,082)
Net periodic benefit costs	143	244
Pension Benefits | Non- U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	1,173	1,126
Estimated fair value of plan assets	564	488
Over (under) funded status	(609)	(638)
Net periodic benefit costs	103	92
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	1,252	1,289	1,324
Estimated fair value of plan assets	1,492	1,468	1,360
Over (under) funded status	240	179
Net periodic benefit costs	(92)	(67)	$ (64)
Other Postretirement Benefits | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	1,208	1,247
Estimated fair value of plan assets	1,465	1,441
Over (under) funded status	257	194
Net periodic benefit costs	(94)	(70)
Other Postretirement Benefits | Non- U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	44	42
Estimated fair value of plan assets	27	27
Over (under) funded status	(17)	(15)
Net periodic benefit costs	$ 2	$ 3