Long-term Debt and Debt Facility Agreements - Long-term Debt (Parenthetical) (Detail)	3 Months Ended							12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
3.65% Senior Notes due 2023
Debt Instrument [Line Items]
Debt instrument interest rate				3.65%				3.65%	3.65%
Debt instrument maturity date								2023	2023
3.90% Senior Notes due 2028
Debt Instrument [Line Items]
Debt instrument interest rate				3.90%		3.90%		3.90%	3.90%
Debt instrument maturity date						2028		2028	2028
1.375% Notes due 2026
Debt Instrument [Line Items]
Debt instrument interest rate		1.375%		1.375%				1.375%	1.375%
Debt instrument maturity date		2026						2026	2026
2.0% Notes due 2032
Debt Instrument [Line Items]
Debt instrument interest rate		2.00%		2.00%				2.00%	2.00%
Debt instrument maturity date		2032						2032	2032
0.25% Notes due 2027
Debt Instrument [Line Items]
Debt instrument interest rate			0.25%	0.25%	0.25%			0.25%	0.25%
Debt instrument maturity date			2027		2027			2027	2027
0.50% Notes due 2031
Debt Instrument [Line Items]
Debt instrument interest rate			0.50%	0.50%	0.50%			0.50%	0.50%
Debt instrument maturity date			2031		2031			2031	2031
2.65% Senior Notes due 2030
Debt Instrument [Line Items]
Debt instrument interest rate		2.65%		2.65%				2.65%	2.65%
Debt instrument maturity date		2030						2030	2030
2.40% Senior Notes due 2022
Debt Instrument [Line Items]
Debt instrument interest rate				2.40%				2.40%	2.40%
Debt instrument maturity date								2022	2022
4.00% Senior Notes due 2025
Debt Instrument [Line Items]
Debt instrument interest rate				4.00%				4.00%	4.00%
Debt instrument maturity date								2025	2025
4.30% Senior Notes due 2029
Debt Instrument [Line Items]
Debt instrument interest rate				4.30%			4.30%	4.30%	4.30%
Debt instrument maturity date							2029	2029	2029
3.75% Senior Notes due 2024
Debt Instrument [Line Items]
Debt instrument interest rate				3.75%			3.75%	3.75%	3.75%
Debt instrument maturity date							2024	2024	2024
1.00% Guaranteed Notes due 2026
Debt Instrument [Line Items]
Debt instrument interest rate				1.00%				1.00%	1.00%
Debt instrument maturity date								2026	2026
0.00% Notes due 2024
Debt Instrument [Line Items]
Debt instrument interest rate				0.00%	0.00%			0.00%	0.00%
Debt instrument maturity date					2024			2024	2024
2.65% Senior Notes due 2022
Debt Instrument [Line Items]
Debt instrument interest rate				2.65%				2.65%	2.65%
Debt instrument maturity date								2022	2022
1.40% Senior Notes due 2025
Debt Instrument [Line Items]
Debt instrument interest rate	1.40%			1.40%				1.40%	1.40%
Debt instrument maturity date	2025							2025	2025
3.63% Senior Notes due 2022
Debt Instrument [Line Items]
Debt instrument interest rate				3.63%		3.63%		3.63%	3.63%
Debt instrument maturity date						2022		2022	2022
7.00% Notes due 2038
Debt Instrument [Line Items]
Debt instrument interest rate				7.00%				7.00%	7.00%
Debt instrument maturity date								2038	2038
4.00% Notes due 2023
Debt Instrument [Line Items]
Debt instrument interest rate				4.00%				4.00%	4.00%
Debt instrument maturity date								2023	2023
5.95% Notes due 2041
Debt Instrument [Line Items]
Debt instrument interest rate				5.95%				5.95%	5.95%
Debt instrument maturity date								2041	2041
5.13% Notes due 2043
Debt Instrument [Line Items]
Debt instrument interest rate				5.13%				5.13%	5.13%
Debt instrument maturity date								2043	2043
3.70% Notes due 2024
Debt Instrument [Line Items]
Debt instrument interest rate				3.70%				3.70%	3.70%
Debt instrument maturity date								2024	2024
3.30% Senior Notes due 2021
Debt Instrument [Line Items]
Debt instrument interest rate		3.30%		3.30%				3.30%	3.30%
Debt instrument maturity date		2021						2021	2021
4.20% Senior Notes due 2021
Debt Instrument [Line Items]
Debt instrument interest rate		4.20%		4.20%				4.20%	4.20%
Debt instrument maturity date		2021		2021				2021	2021