Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument
Medium-term notes, maximum remaining maturity	9 years
Long-term debt	$ 22,815	$ 22,106
Long-term debt outstanding maturity:
2019	5,820
2020	6,407
2021	4,884
2022	2,053
2023	2,158
Thereafter	1,493
Total	22,815	22,106
Medium-term notes, callable	238
Medium-term notes
Debt Instrument
Long-term debt issued	6,840
Long-term debt issued at fixed interest rates	3,790
Long-term debt issued at floating interest rates	3,050
Long term debt, gross	22,226	21,362
Unamortized discount and debt issuance costs	(57)	(59)
Long-term debt	$ 22,169	$ 21,303
Long-term debt, Avg. Rate	2.60%	2.50%
Long-term debt outstanding maturity:
Total	$ 22,169	$ 21,303
Bank borrowings
Debt Instrument
Long-term debt	$ 646	$ 803
Long-term debt, Avg. Rate	5.80%	5.00%
Long-term debt outstanding maturity:
Total	$ 646	$ 803