Employee Benefit Obligations - Weighted Average Assumptions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Weighted-average assumptions used to determine net periodic benefit cost
Pension expense		$ 47
Curtailment and settlement losses including special termination benefits		$ 8
Corridor percentage considered for amortization of accumulated actuarial gains and losses		10.00%
Forecast
Weighted-average assumptions used to determine net periodic benefit cost
Pension expense	$ 49
Defined Benefit Pension Plans
Weighted-average assumptions used to determine benefit obligations
Effect of one quarter of a percentage point reduction in the expected return on pension assets assumption, on pension expense		$ 14
Effect of quarter of a percentage point reduction in the discount rate applied to the pension liability, on pension expense		1
Weighted-average assumptions used to determine net periodic benefit cost
Pension expense		48	$ 98	$ 135
Curtailment and settlement losses including special termination benefits		8	36	46
Market related value of plan assets used to calculate expected return		$ 5,375	$ 6,052	$ 6,121
US Plan | Defined Benefit Pension Plans
Weighted-average assumptions used to determine benefit obligations
Discount rate (as a percent)		3.35%	4.41%	3.72%
Rate of compensation increase (as a percent)		4.03%	4.02%	4.15%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)		4.41%	3.72%	4.27%
Rate of compensation increase (as a percent)		4.02%	4.15%	4.14%
Expected long-term rate of return on assets (as a percent)		5.58%	5.14%	5.50%
Pension expense		$ 59	$ 115	$ 132
Curtailment and settlement losses including special termination benefits			36	47
Foreign | Defined Benefit Pension Plans
Weighted-average assumptions used to determine net periodic benefit cost
Pension expense		(11)	$ (17)	3
Curtailment and settlement losses including special termination benefits		$ 8		$ (1)
U.K. | Defined Benefit Pension Plans
Weighted-average assumptions used to determine benefit obligations
Discount rate (as a percent)		2.07%	2.90%	2.55%
Rate of compensation increase (as a percent)		3.50%	3.50%	4.41%
Pension increase (as a percent)		3.22%	3.45%	3.41%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)		2.90%	2.55%	2.70%
Rate of compensation increase (as a percent)		3.50%	4.41%	4.30%
Pension increase (as a percent)		3.45%	3.41%	3.41%
Expected long-term rate of return on assets (as a percent)		3.40%	3.05%	3.20%
Germany | Defined Benefit Pension Plans
Weighted-average assumptions used to determine benefit obligations
Discount rate (as a percent)		1.11%	1.74%	1.68%
Rate of compensation increase (as a percent)		2.50%	2.50%	2.50%
Pension increase (as a percent)		1.50%	1.50%	1.50%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)		1.74%	1.68%	1.52%
Rate of compensation increase (as a percent)		2.50%	2.50%	2.50%
Pension increase (as a percent)		1.50%	1.50%	1.50%