Long-term Debt - Long-term Debt (Parenthetical) (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
3.30% Senior Notes due 2021
Debt Instrument [Line Items]
Debt instrument interest rate	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%
Debt instrument maturity date	2023	2023
4.20% Senior Notes due 2021
Debt Instrument [Line Items]
Debt instrument interest rate	4.20%	4.20%
Debt instrument maturity date	2021	2021
1.25% Senior Notes due 2017
Debt Instrument [Line Items]
Debt instrument interest rate	1.25%	1.25%
Debt instrument maturity date	2017	2017
2.40% Senior Notes due 2022
Debt Instrument [Line Items]
Debt instrument interest rate	2.40%	2.40%
Debt instrument maturity date	2022	2022
1.50% Guaranteed Notes due 2019
Debt Instrument [Line Items]
Debt instrument interest rate	1.50%	1.50%
Debt instrument maturity date	2019	2019
1.95% Senior Notes due 2016
Debt Instrument [Line Items]
Debt instrument interest rate	1.95%	1.95%
Debt instrument maturity date	2016	2016
2.65% Senior Notes due 2016
Debt Instrument [Line Items]
Debt instrument interest rate	2.65%	2.65%
Debt instrument maturity date	2016	2016