Borrowings - Schedule of Borrowings (Details) - USD ($) $ in Millions	Sep. 30, 2020	Aug. 31, 2020	Aug. 21, 2020	Mar. 31, 2020	Dec. 31, 2019	Aug. 31, 2019
Debt Instrument [Line Items]
Finance lease obligations	$ 1,036				$ 808
Total debt principal	67,721				69,246
Debt premiums	245				262
Debt discounts and deferred financing costs	(971)				(1,028)
Long-term debt and lease obligation	66,995				68,480
Current portion of long-term debt	(5,443)				(3,781)
Long-term debt	61,552				$ 64,699
Senior Notes | 3.125% senior notes due March 2020
Debt Instrument [Line Items]
Debt interest rate					3.125%	3.125%
Long-term debt	0				$ 723
Senior Notes | 2.8% senior notes due July 2020
Debt Instrument [Line Items]
Debt interest rate					2.80%
Long-term debt	$ 0				$ 2,750
Senior Notes | 3.35% senior notes due March 2021
Debt Instrument [Line Items]
Debt interest rate	3.35%					3.35%
Long-term debt	$ 2,038				2,038
Senior Notes | 4.125% senior notes due May 2021
Debt Instrument [Line Items]
Debt interest rate	4.125%					4.125%
Long-term debt	$ 222				222
Senior Notes | 2.125% senior notes due June 2021
Debt Instrument [Line Items]
Debt interest rate	2.125%
Long-term debt	$ 1,750				1,750
Senior Notes | 4.125% senior notes due June 2021
Debt Instrument [Line Items]
Debt interest rate	4.125%					4.125%
Long-term debt	$ 203				203
Senior Notes | 5.45% senior notes due June 2021
Debt Instrument [Line Items]
Debt interest rate	5.45%					5.45%
Long-term debt	$ 187				187
Senior Notes | 3.5% senior notes due July 2022
Debt Instrument [Line Items]
Debt interest rate	3.50%
Long-term debt	$ 1,500				1,500
Senior Notes | 2.75% senior notes due November 2022
Debt Instrument [Line Items]
Debt interest rate	2.75%
Long-term debt	$ 1,000				1,000
Senior Notes | 2.75% senior notes due December 2022
Debt Instrument [Line Items]
Debt interest rate	2.75%
Long-term debt	$ 1,250				1,250
Senior Notes | 4.75% senior notes due December 2022
Debt Instrument [Line Items]
Debt interest rate	4.75%
Long-term debt	$ 399				399
Senior Notes | 3.7% senior notes due March 2023
Debt Instrument [Line Items]
Debt interest rate	3.70%	3.70%
Long-term debt	$ 3,723				6,000
Senior Notes | 2.8% senior notes due June 2023
Debt Instrument [Line Items]
Debt interest rate	2.80%
Long-term debt	$ 1,300				1,300
Senior Notes | 4% senior notes due December 2023
Debt Instrument [Line Items]
Debt interest rate	4.00%	4.00%
Long-term debt	$ 527				1,250
Senior Notes | 3.375% senior notes due August 2024
Debt Instrument [Line Items]
Debt interest rate	3.375%
Long-term debt	$ 650				650
Senior Notes | 2.625% senior notes due August 2024
Debt Instrument [Line Items]
Debt interest rate	2.625%
Long-term debt	$ 1,000				1,000
Senior Notes | 3.5% senior notes due November 2024
Debt Instrument [Line Items]
Debt interest rate	3.50%
Long-term debt	$ 750				750
Senior Notes | 5% senior notes due December 2024
Debt Instrument [Line Items]
Debt interest rate	5.00%
Long-term debt	$ 299				299
Senior Notes | 4.1% senior notes due March 2025
Debt Instrument [Line Items]
Debt interest rate	4.10%	4.10%
Long-term debt	$ 2,000				5,000
Senior Notes | 3.875% senior notes due July 2025
Debt Instrument [Line Items]
Debt interest rate	3.875%
Long-term debt	$ 2,828				2,828
Senior Notes | 2.875% senior notes due June 2026
Debt Instrument [Line Items]
Debt interest rate	2.875%
Long-term debt	$ 1,750				1,750
Senior Notes | 3% senior notes due August 2026
Debt Instrument [Line Items]
Debt interest rate	3.00%
Long-term debt	$ 750				750
Senior Notes | 3.625% senior notes due April 2027
Debt Instrument [Line Items]
Debt interest rate	3.625%			3.625%
Long-term debt	$ 750				0
Senior Notes | 6.25% senior notes due June 2027
Debt Instrument [Line Items]
Debt interest rate	6.25%
Long-term debt	$ 372				372
Senior Notes | 1.3% senior notes due August 2027
Debt Instrument [Line Items]
Debt interest rate	1.30%		1.30%
Long-term debt	$ 1,500				0
Senior Notes | 4.3% senior notes due March 2028
Debt Instrument [Line Items]
Debt interest rate	4.30%
Long-term debt	$ 9,000				9,000
Senior Notes | 3.25% senior notes due August 2029
Debt Instrument [Line Items]
Debt interest rate	3.25%
Long-term debt	$ 1,750				1,750
Senior Notes | 3.75% senior notes due April 2030
Debt Instrument [Line Items]
Debt interest rate	3.75%			3.75%
Long-term debt	$ 1,500				0
Senior Notes | 1.75% senior notes due August 2030
Debt Instrument [Line Items]
Debt interest rate	1.75%		1.75%
Long-term debt	$ 1,250				0
Senior Notes | 4.875% senior notes due July 2035
Debt Instrument [Line Items]
Debt interest rate	4.875%
Long-term debt	$ 652				652
Senior Notes | 6.625% senior notes due June 2036
Debt Instrument [Line Items]
Debt interest rate	6.625%
Long-term debt	$ 771				771
Senior Notes | 6.75% senior notes due December 2037
Debt Instrument [Line Items]
Debt interest rate	6.75%
Long-term debt	$ 533				533
Senior Notes | 4.78% senior notes due March 2038
Debt Instrument [Line Items]
Debt interest rate	4.78%
Long-term debt	$ 5,000				5,000
Senior Notes | 6.125% senior notes due September 2039
Debt Instrument [Line Items]
Debt interest rate	6.125%
Long-term debt	$ 447				447
Senior Notes | 4.125% senior notes due April 2040
Debt Instrument [Line Items]
Debt interest rate	4.125%			4.125%
Long-term debt	$ 1,000				0
Senior Notes | 2.7% senior notes due August 2040
Debt Instrument [Line Items]
Debt interest rate	2.70%		2.70%
Long-term debt	$ 1,250				0
Senior Notes | 5.75% senior notes due May 2041
Debt Instrument [Line Items]
Debt interest rate	5.75%
Long-term debt	$ 133				133
Senior Notes | 4.5% senior notes due May 2042
Debt Instrument [Line Items]
Debt interest rate	4.50%
Long-term debt	$ 500				500
Senior Notes | 4.125% senior notes due November 2042
Debt Instrument [Line Items]
Debt interest rate	4.125%
Long-term debt	$ 500				500
Senior Notes | 5.3% senior notes due December 2043
Debt Instrument [Line Items]
Debt interest rate	5.30%
Long-term debt	$ 750				750
Senior Notes | 4.75% senior notes due March 2044
Debt Instrument [Line Items]
Debt interest rate	4.75%
Long-term debt	$ 375				375
Senior Notes | 5.125% senior notes due July 2045
Debt Instrument [Line Items]
Debt interest rate	5.125%
Long-term debt	$ 3,500				3,500
Senior Notes | 3.875% senior notes due August 2047
Debt Instrument [Line Items]
Debt interest rate	3.875%
Long-term debt	$ 1,000				1,000
Senior Notes | 5.05% senior notes due March 2048
Debt Instrument [Line Items]
Debt interest rate	5.05%
Long-term debt	$ 8,000				8,000
Senior Notes | 4.25% senior notes due April 2050
Debt Instrument [Line Items]
Debt interest rate	4.25%			4.25%
Long-term debt	$ 750				$ 0
Floating Rate Notes | Floating rate notes due March 2020 (2.515% at December 31, 2019)
Debt Instrument [Line Items]
Debt interest rate					2.515%
Long-term debt	$ 0				$ 277
Floating Rate Notes | Floating rate notes due March 2021 (0.968% at September 30, 2020 and 2.605% at December 31, 2019)
Debt Instrument [Line Items]
Debt interest rate	0.968%				2.605%
Long-term debt	$ 1,000				$ 1,000
Other Debt Obligations
Debt Instrument [Line Items]
Long-term debt	$ 276				$ 279