Debt - Summary of Debt Instruments (Parenthetical) (Detail)	Sep. 30, 2018	Apr. 02, 2018	Mar. 19, 2018	Dec. 31, 2017
Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate		2.00%	3.70%
2.0% [Member] | Due in 2018 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	2.00%			2.00%
4.625% [Member] | Due in 2019 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.625%			4.625%
2.7% [Member] | Due in 2020 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	2.70%			2.70%
3.375% [Member] | Due in 2021 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	3.375%			3.375%
3.150% [Member] | Due in 2022 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	3.15%			3.15%
3.7% [Member] | Due in 2023 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	3.70%			3.70%
3.550% [Member] | Due in 2025 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	3.55%			3.55%
4.250% [Member] | Due in 2035 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.25%			4.25%
5.750% [Member] | Due in 2039 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	5.75%			5.75%
4.450% [Member] | Due in 2045 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate	4.45%			4.45%
1.414% [Member] | Due in 2022 [Member] | Euro Notes [Member]
Debt Instrument [Line Items]
Interest rate	1.414%			1.414%
2.425% [Member] | Due in 2026 [Member] | Euro Notes [Member]
Debt Instrument [Line Items]
Interest rate	2.425%			2.425%