Long-Term Debt and Short-Term Borrowings - Long-Term Debt (Details) € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2020 EUR (€)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Aug. 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2004 USD ($)
Long-Term Debt
Total long-term debt	$ 18,783			$ 19,359
Long-term debt (excluding current portion)	17,989			17,518
Third lien senior secured notes subject to in-substance defeasance (repaid in 2020)
Long-Term Debt
Total long-term debt				463
Floating rate Euro medium term note (repaid in 2020)
Long-Term Debt
Total long-term debt				726
Floating rate medium term note (repaid in 2020)
Long-Term Debt
Total long-term debt				299
Floating rate medium term note (repaid in 2020)
Long-Term Debt
Total long-term debt				200
Fixed rate medium term note (repaid in 2020)
Long-Term Debt
Principal amount	400
Total long-term debt				599
Fixed rate medium term note (repaid in 2020)
Long-Term Debt
Principal amount	$ 600
Total long-term debt				199
Floating rate medium term note (repaid in 2020)
Long-Term Debt
Total long-term debt				204
Floating rate Eurobond due 2021
Long-Term Debt
Principal amount | €		€ 300
Interest rate - effective	(0.28%)
Total long-term debt	$ 374			346
Fixed rate Eurobond due 2021
Long-Term Debt
Principal amount | €		€ 300
Interest rate - effective	1.97%	1.97%
Total long-term debt	$ 367			334
Fixed rate Euro medium term note due 2022
Long-Term Debt
Principal amount | €		€ 500
Interest rate - effective	0.45%	0.45%
Total long-term debt	$ 612			557
Fixed rate medium term note due 2022
Long-Term Debt
Principal amount	$ 600					$ 450
Interest rate - effective	2.17%	2.17%				2.75%
Total long-term debt	$ 598			597
Fixed rate medium term note due 2022
Long-Term Debt
Principal amount	$ 450
Interest rate - effective	2.76%	2.76%
Total long-term debt	$ 449			449
Fixed rate Euro medium term note due 2023
Long-Term Debt
Principal amount | €		€ 600
Interest rate - effective	1.14%	1.14%
Total long-term debt	$ 731			665
Fixed rate medium term notes due 2023
Long-Term Debt
Principal amount	$ 650
Interest rate - effective	2.26%	2.26%
Total long-term debt	$ 649			648
Fixed rate registered note due 2023
Long-Term Debt
Principal amount	$ 500				$ 500
Interest rate - effective	1.86%	1.86%			1.75%
Total long-term debt	$ 498			497
Floating rate medium term notes due 2024
Long-Term Debt
Principal amount	$ 300						$ 300
Interest rate - effective	0.52%	0.52%
Total long-term debt	$ 299			299
Fixed rate medium term notes due 2024
Long-Term Debt
Principal amount	$ 300						$ 300
Interest rate - effective	3.30%	3.30%					3.25%
Total long-term debt	$ 299			299
Fixed rate medium term notes due 2024
Long-Term Debt
Principal amount	$ 500					$ 500
Interest rate - effective	2.98%	2.98%				3.25%
Total long-term debt	$ 502			503
Fixed rate medium term note due 2025
Long-Term Debt
Principal amount	$ 550
Interest rate - effective	3.04%	3.04%
Total long-term debt	$ 548			547
Fixed rate registered note due 2025
Long-Term Debt
Principal amount	$ 750		$ 500		$ 750
Interest rate - effective	2.12%	2.12%	2.65%		2.00%
Total long-term debt	$ 744			743
Fixed rate registered note due 2025
Long-Term Debt
Principal amount	$ 500
Interest rate - effective	2.67%	2.67%
Total long-term debt	$ 498
Fixed rate Euro medium term note due 2026
Long-Term Debt
Principal amount | €		€ 750
Interest rate - effective	1.66%	1.66%
Total long-term debt	$ 908			826
Fixed rate medium term notes due 2026
Long-Term Debt
Principal amount	$ 650
Interest rate - effective	2.37%	2.37%
Total long-term debt	$ 644			643
Fixed rate medium term notes due 2027
Long-Term Debt
Principal amount	$ 850
Interest rate - effective	2.95%	2.95%
Total long-term debt	$ 843			842
Fixed rate 30-year debenture due 2028
Long-Term Debt
Principal amount	$ 220
Interest rate - effective	6.44%	6.44%
Total long-term debt	$ 225			226
Fixed rate medium term notes due 2028
Long-Term Debt
Principal amount	$ 600						$ 600
Interest rate - effective	3.62%	3.62%					3.625%
Total long-term debt	$ 598			597
Fixed rate medium term notes due 2029
Long-Term Debt
Principal amount	$ 800					$ 800
Interest rate - effective	3.38%	3.38%				3.375%
Total long-term debt	$ 796			796
Fixed rate registered note due 2029
Long-Term Debt
Principal amount	$ 1,000				$ 1,000
Interest rate - effective	2.50%	2.50%			2.375%
Total long-term debt	$ 986			984
Fixed rate Euro medium term note due 2030
Long-Term Debt
Principal amount | €		€ 500
Interest rate - effective	1.90%	1.90%
Total long-term debt	$ 604			549
Fixed rate registered note due 2030
Long-Term Debt
Principal amount	$ 600		$ 600
Interest rate - effective	3.09%	3.09%	3.05%
Total long-term debt	$ 595
Fixed rate Euro medium term notes due 2031
Long-Term Debt
Principal amount | €		€ 500
Interest rate - effective	1.54%	1.54%
Total long-term debt	$ 608			554
Fixed rate 30-year bond due 2037
Long-Term Debt
Principal amount	$ 555
Interest rate - effective	5.73%	5.73%
Total long-term debt	$ 551			551
Floating rate note due 2041
Long-Term Debt
Principal amount	96
Total long-term debt	96			96
Fixed rate medium term note due 2044
Long-Term Debt
Principal amount	$ 325
Interest rate - effective	4.05%	4.05%
Total long-term debt	$ 315			314
Floating rate note due 2044
Long-Term Debt
Principal amount	55							$ 60
Total long-term debt	53			53
Fixed rate medium term note due 2046
Long-Term Debt
Principal amount	$ 500
Interest rate - effective	3.37%	3.37%
Total long-term debt	$ 476			475
Fixed rate medium term note due 2047
Long-Term Debt
Principal amount	$ 500
Interest rate - effective	3.68%	3.68%
Total long-term debt	$ 492			492
Fixed rate medium term note due 2048
Long-Term Debt
Principal amount	$ 650						$ 650
Interest rate - effective	4.07%	4.07%					4.00%
Total long-term debt	$ 637			637
Fixed rate medium term note due 2048
Long-Term Debt
Principal amount	$ 500					$ 500
Interest rate - effective	3.78%	3.78%				4.00%
Total long-term debt	$ 505			506
Fixed rate registered note due 2049
Long-Term Debt
Principal amount	$ 1,000				$ 1,000
Interest rate - effective	3.37%	3.37%			3.25%
Total long-term debt	$ 969			968
Fixed rate registered note due 2050
Long-Term Debt
Principal amount	$ 650		$ 650
Interest rate - effective	3.72%	3.72%	3.70%
Total long-term debt	$ 642
Other borrowings
Long-Term Debt
Interest rate - effective	0.01%	0.01%
Total long-term debt	$ 72			76
Current portion of long-term debt
Long-Term Debt
Interest rate - effective	0.78%	0.78%
Total long-term debt	$ 794			$ 1,841