Borrowings - Short-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Short-term debt disclosures
Long-term debt - current maturities	$ 7,106	$ 7,051
Total short-term debt	10,250	10,207
Commercial paper
Short-term debt disclosures
Short-term debt	$ 2,993	$ 2,995
Weighted-average interest rates for short-term debt (as a percent)	2.50%	2.50%
Short-term loans
Short-term debt disclosures
Short-term debt	$ 150	$ 161
Weighted-average interest rates for short-term debt (as a percent)	5.80%	4.30%