Fair Value Measurements - Estimated Fair Value of Senior Notes (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2013
5.375% Senior Notes Due 2014 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes, maturity date	2014
Senior Notes, interest rate	5.375%
5.375% Senior Notes Due 2015 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes, maturity date	2015
Senior Notes, interest rate	5.375%
5.625% Senior Notes Due 2020 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes, maturity date	2020
Senior Notes, interest rate	5.625%
6.000% Senior Notes due 2043 [Member]
Schedule Of Fair Value Of Senior Notes [Line Items]
Senior Notes, maturity date	2043
Senior Notes, interest rate	6.00%