Borrowings - Short-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Short-term debt disclosures
Long-term debt - current maturities	$ 3,758	$ 5,214
Total short-term debt	5,977	6,987
Commercial paper
Short-term debt disclosures
Short-term debt	$ 1,997	$ 1,496
Weighted-average interest rates for short-term debt (as a percent)	1.80%	1.50%
Short-term loans
Short-term debt disclosures
Short-term debt	$ 221	$ 276
Weighted-average interest rates for short-term debt (as a percent)	7.60%	8.80%