Long-Term Debt and Short-Term Borrowings - Post-Swap Borrowing, Long-Term Debt, Including Current Portion (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Long-Term Debt
Total long-term debt	$ 18,783	$ 19,359
Fixed-rate debt
Long-Term Debt
Interest rate - effective	2.80%	3.01%
Total long-term debt	$ 17,889	$ 17,061
Floating-rate debt
Long-Term Debt
Interest rate - effective	0.06%	1.06%
Total long-term debt	$ 894	$ 2,298