Long-Term Debt and Short-Term Borrowings - Short-Term Borrowings and Current Portion of Long-Term Debt (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Short-Term Borrowings and Current Portion of Long-Term Debt
Short-term borrowings and current portion of long-term debt	$ 3,225	$ 1,853
Commercial paper
Short-Term Borrowings and Current Portion of Long-Term Debt
Short-term borrowings and current portion of long-term debt	$ 1,500	$ 745