Credit Agreement and Senior Notes - Summary of Carrying Value of Senior Notes (Parenthetical) (Detail)	Dec. 31, 2013	Dec. 31, 2012
5.15% Senior Notes due 2014 [Member]
Debt Instrument [Line Items]
Interest rate of senior notes	5.15%	5.15%
4.875% Senior Notes due 2015 [Member]
Debt Instrument [Line Items]
Interest rate of senior notes	4.875%	4.875%
5.875% Senior Notes due 2019 [Member]
Debt Instrument [Line Items]
Interest rate of senior notes	5.875%	5.875%
3.45% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Interest rate of senior notes	3.45%
5.70% Senior Notes due 2039 [Member]
Debt Instrument [Line Items]
Interest rate of senior notes	5.70%	5.70%
4.875% Senior Notes due 2043 [Member]
Debt Instrument [Line Items]
Interest rate of senior notes	4.875%