Short-Term Borrowings (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt
Short-term borrowings, Balance	$ 4,836	$ 7,094
Commercial paper, net
Short-term Debt
Short-term borrowings, Balance	$ 3,680	$ 5,985
Short-term borrowings, Avg. Rate	1.10%	0.90%
Bank borrowings
Short-term Debt
Short-term borrowings, Balance	$ 675	$ 553
Short-term borrowings, Avg. Rate	5.20%	7.50%
Variable denomination floating rate demand notes
Short-term Debt
Short-term borrowings, Balance	$ 481	$ 556
Short-term borrowings, Avg. Rate	1.10%	0.90%