Debt - Outstanding Amounts of Debt and Finance Leases (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Short-term debt
Commercial paper	$ 1,555,000,000	$ 944,000,000
Other, including finance leases	20,000,000	27,000,000
Total short-term debt	6,449,000,000	5,514,000,000
Long-term debt
Other, including finance leases	40,000,000	61,000,000
Total long-term debt	29,537,000,000	31,893,000,000
$1,000 million, Floating Rate Notes due 3/2020
Short-term debt
Current maturities	0	999,000,000
Long-term debt
Face value	1,000,000,000
$300 million, 5.125% Notes due 6/2020
Short-term debt
Current maturities	0	300,000,000
Long-term debt
Face value	$ 300,000,000
Stated interest rate	5.125%
$1,750 million, 3.2% Notes due 9/2020
Short-term debt
Current maturities	$ 0	1,748,000,000
Long-term debt
Face value	$ 1,750,000,000
Stated interest rate	3.20%
$349 million, 4.125% Notes due 9/2020
Short-term debt
Current maturities	$ 0	351,000,000
Long-term debt
Face value	$ 349,000,000
Stated interest rate	4.125%
$500 million, 2.6% Notes due 11/2020
Short-term debt
Current maturities	$ 500,000,000	496,000,000
Long-term debt
Face value	$ 500,000,000
Stated interest rate	2.60%
$400 million, Floating Rate Notes due 11/2020
Short-term debt
Current maturities	$ 400,000,000	400,000,000
Long-term debt
Face value	400,000,000
$250 million, 4.375% Notes due 12/2020
Short-term debt
Current maturities	250,000,000	249,000,000
Long-term debt
Face value	$ 250,000,000
Stated interest rate	4.375%
$1,400 million, Floating Rate Term Loan due 3/2021
Short-term debt
Current maturities	$ 1,399,000,000	0
Long-term debt
Face value	1,400,000,000
$78 million, 6.37% Notes due 6/2021
Short-term debt
Current maturities	78,000,000	0
Long-term debt
Long-term debt	0	78,000,000
Face value	$ 78,000,000
Stated interest rate	6.37%
$1,000 million, Floating Rate Notes due 2021
Short-term debt
Current maturities	$ 999,000,000	0
Long-term debt
Long-term debt	0	998,000,000
Face value	1,000,000,000
$1,250 million, 3.4% Notes due 2021
Short-term debt
Current maturities	1,248,000,000	0
Long-term debt
Long-term debt	0	1,247,000,000
Face value	$ 1,250,000,000
Stated interest rate	3.40%
$500 million, 3.3% Notes due 2021
Long-term debt
Long-term debt	$ 0	499,000,000
Face value	$ 500,000,000
Stated interest rate	3.30%
$300 million, 4.5% Notes due 2021
Long-term debt
Long-term debt	$ 0	298,000,000
Face value	$ 300,000,000
Stated interest rate	4.50%
$1,248 million, 4.75% Notes due 2021
Long-term debt
Long-term debt	$ 0	1,272,000,000
Face value	$ 1,248,000,000
Stated interest rate	4.75%
$277 million, 4% Notes due 2022
Long-term debt
Long-term debt	$ 276,000,000	747,000,000
Face value	$ 277,000,000
Stated interest rate	4.00%
$973 million, 3.9% Notes due 2022
Long-term debt
Long-term debt	$ 972,000,000	999,000,000
Face value	$ 973,000,000
Stated interest rate	3.90%
$500 million, 3.05% Notes due 2022
Long-term debt
Long-term debt	$ 489,000,000	485,000,000
Face value	$ 500,000,000
Stated interest rate	3.05%
$17 million, 8.3% Notes due 2023
Long-term debt
Long-term debt	$ 17,000,000	17,000,000
Face value	$ 17,000,000
Stated interest rate	8.30%
$63 million, 7.65% Notes due 2023
Long-term debt
Long-term debt	$ 63,000,000	100,000,000
Face value	$ 63,000,000
Stated interest rate	7.65%
$700 million, Floating Rate Notes due 2023
Long-term debt
Long-term debt	$ 698,000,000	698,000,000
Face value	700,000,000
$1,000 million, 3% Notes due 2023
Long-term debt
Long-term debt	973,000,000	966,000,000
Face value	$ 1,000,000,000
Stated interest rate	3.00%
$2,187 million, 3.75% Notes due 2023
Long-term debt
Long-term debt	$ 2,180,000,000	3,088,000,000
Face value	$ 2,187,000,000
Stated interest rate	3.75%
$1,000 million, 3.5% Notes due 2024
Long-term debt
Long-term debt	$ 976,000,000	970,000,000
Face value	$ 1,000,000,000
Stated interest rate	3.50%
$900 million, 3.25% Notes due 2025
Long-term debt
Long-term debt	$ 896,000,000	895,000,000
Face value	$ 900,000,000
Stated interest rate	3.25%
$2,200 million, 4.125% Notes due 2025
Long-term debt
Long-term debt	$ 2,189,000,000	2,188,000,000
Face value	$ 2,200,000,000
Stated interest rate	4.125%
$1,500 million, 4.5% Notes due 2026
Long-term debt
Long-term debt	$ 1,505,000,000	1,506,000,000
Face value	$ 1,500,000,000
Stated interest rate	4.50%
$1,500 million, 3.4% Notes due 2027
Long-term debt
Long-term debt	$ 1,406,000,000	1,396,000,000
Face value	$ 1,500,000,000
Stated interest rate	3.40%
$259 million, 7.875% Debentures due 2027
Long-term debt
Long-term debt	$ 259,000,000	259,000,000
Face value	$ 259,000,000
Stated interest rate	7.875%
$600 million, 3.05% Notes due 2027
Long-term debt
Long-term debt	$ 595,000,000	595,000,000
Face value	$ 600,000,000
Stated interest rate	3.05%
$3,800 million, 4.375% Notes due 2028
Long-term debt
Long-term debt	$ 3,779,000,000	3,776,000,000
Face value	$ 3,800,000,000
Stated interest rate	4.375%
$1,500 million, 2.4% Notes due 2030
Long-term debt
Long-term debt	$ 1,489,000,000	0
Face value	$ 1,500,000,000
Stated interest rate	2.40%
$45 million, 8.3% Step Down Notes due 2033
Long-term debt
Long-term debt	$ 45,000,000	45,000,000
Face value	$ 45,000,000
Stated interest rate	8.30%
$190 million, 6.15% Notes due 2036
Long-term debt
Long-term debt	$ 190,000,000	190,000,000
Face value	$ 190,000,000
Stated interest rate	6.15%
$2,200 million, 4.8% Notes due 2038
Long-term debt
Long-term debt	$ 2,180,000,000	2,178,000,000
Face value	$ 2,200,000,000
Stated interest rate	4.80%
$750 million, 3.2% Notes due 2040
Long-term debt
Long-term debt	$ 742,000,000	0
Face value	$ 750,000,000
Stated interest rate	3.20%
$121 million, 5.875% Notes due 2041
Long-term debt
Long-term debt	$ 119,000,000	119,000,000
Face value	$ 121,000,000
Stated interest rate	5.875%
$448 million, 6.125% Notes due 2041
Long-term debt
Long-term debt	$ 490,000,000	491,000,000
Face value	$ 448,000,000
Stated interest rate	6.125%
$317 million, 5.375% Notes due 2042
Long-term debt
Long-term debt	$ 315,000,000	315,000,000
Face value	$ 317,000,000
Stated interest rate	5.375%
$1,500 million, 4.8% Notes due 2046
Long-term debt
Long-term debt	$ 1,465,000,000	1,465,000,000
Face value	$ 1,500,000,000
Stated interest rate	4.80%
$1,000 million, 3.875% Notes due 2047
Long-term debt
Long-term debt	$ 988,000,000	988,000,000
Face value	$ 1,000,000,000
Stated interest rate	3.875%
$3,000 million, 4.9% Notes due 2048
Long-term debt
Long-term debt	$ 2,966,000,000	2,964,000,000
Face value	$ 3,000,000,000
Stated interest rate	4.90%
$1,250 million, 3.4% Notes due 2050
Long-term debt
Long-term debt	$ 1,235,000,000	$ 0
Face value	$ 1,250,000,000
Stated interest rate	3.40%