Debt - Summary of Debt (Non-Printing) (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Aug. 31, 2019
Debt Instrument [Line Items]
Interest rate			3.85%
2.60% senior notes due 2019
Debt Instrument [Line Items]
Interest rate	2.60%	2.60%
Maturity year	2019	2019
3.15% senior notes due 2021
Debt Instrument [Line Items]
Interest rate	3.15%	3.15%
Maturity year	2021	2021
3.75% senior notes due 2021
Debt Instrument [Line Items]
Interest rate	3.75%	3.75%
Maturity year	2021	2021
3.85% senior notes due 2023
Debt Instrument [Line Items]
Interest rate	3.85%	3.85%
Maturity year	2023	2023
3.90% senior notes due 2025
Debt Instrument [Line Items]
Interest rate	3.90%	3.90%	3.90%
Maturity year	2025	2025
4.00% senior notes due 2024
Debt Instrument [Line Items]
Interest rate	4.00%	4.00%	4.00%
Maturity year	2024	2024
4.20% senior notes due 2026
Debt Instrument [Line Items]
Interest rate	4.20%	4.20%
Maturity year	2026	2026
4.00% senior notes due 2022
Debt Instrument [Line Items]
Interest rate	4.00%	4.00%
Maturity year	2022	2022
4.70% senior notes due 2020
Debt Instrument [Line Items]
Interest rate	4.70%	4.70%
Maturity year	2020	2020
5.375% senior notes due 2036
Debt Instrument [Line Items]
Interest rate	5.375%	5.375%
Maturity year	2036	2036
5.50% senior notes due 2046
Debt Instrument [Line Items]
Interest rate	5.50%	5.50%
Maturity year	2046	2046
5.00% senior notes due 2023
Debt Instrument [Line Items]
Interest rate	5.00%	5.00%
Maturity year	2023	2023