Long-term Debt - Summary of Long-term Debt (Parenthetical) (Detail)	1 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Apr. 24, 2019	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
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
3.65% Senior Notes due 2023
Debt Instrument [Line Items]
Debt instrument interest rate	3.65%		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%	3.90%
Debt instrument maturity date		2028		2028	2028
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
2.40% Senior Notes due 2022
Debt Instrument [Line Items]
Debt instrument interest rate	2.40%		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%	4.00%	4.00%
Debt instrument maturity date		2025		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
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
1.00% Guaranteed Notes due 2026
Debt Instrument [Line Items]
Debt instrument interest rate	1.00%		1.00%	1.00%	1.00%
Debt instrument maturity date				2026	2026
2.65% Senior Notes due 2022
Debt Instrument [Line Items]
Debt instrument interest rate	2.65%		2.65%	2.65%	2.65%
Debt instrument maturity date				2022	2022
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
0.25% Notes due 2027
Debt Instrument [Line Items]
Debt instrument interest rate	0.25%		0.25%	0.25%	0.25%
Debt instrument maturity date			2027	2027	2027
0.50% Notes due 2031
Debt Instrument [Line Items]
Debt instrument interest rate	0.50%		0.50%	0.50%	0.50%
Debt instrument maturity date			2031	2031	2031
2.20% Senior Notes due 2020
Debt Instrument [Line Items]
Debt instrument interest rate	2.20%		2.20%	2.20%	2.20%
Debt instrument maturity date				2020	2020
3.00% Senior Notes due 2020
Debt Instrument [Line Items]
Debt instrument interest rate	3.00%		3.00%	3.00%	3.00%
Debt instrument maturity date	2020			2020	2020
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
7.00% Notes due 2038
Debt Instrument [Line Items]
Debt instrument interest rate	7.00%		7.00%	7.00%	7.00%
Debt instrument maturity date				2038	2038
4.50% Notes due 2021
Debt Instrument [Line Items]
Debt instrument interest rate	4.50%		4.50%	4.50%	4.50%
Debt instrument maturity date				2021	2021
5.95% Notes due 2041
Debt Instrument [Line Items]
Debt instrument interest rate	5.95%		5.95%	5.95%	5.95%
Debt instrument maturity date				2041	2041
3.60% Notes due 2022
Debt Instrument [Line Items]
Debt instrument interest rate	3.60%		3.60%	3.60%	3.60%
Debt instrument maturity date				2022	2022
5.13% Notes due 2043
Debt Instrument [Line Items]
Debt instrument interest rate	5.13%		5.13%	5.13%	5.13%
Debt instrument maturity date				2043	2043
4.00% Notes due 2023
Debt Instrument [Line Items]
Debt instrument interest rate	4.00%		4.00%	4.00%	4.00%
Debt instrument maturity date				2023	2023
3.70% Notes due 2024
Debt Instrument [Line Items]
Debt instrument interest rate	3.70%		3.70%	3.70%	3.70%
Debt instrument maturity date				2024	2024