Shares Repurchased (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Share Repurchases [Line Items]
Average repurchase price per share	$ 37.15	$ 26.60	[1]	$ 23.71	[2]
Reverse Split Adjusted Basis
Share Repurchases [Line Items]
Number of shares repurchased		5,300,000		10,300,000
Average repurchase price per share		$ 53.20		$ 47.42

[1] On a reverse split adjusted basis the number of shares repurchased was 5.3 million for $53.20 per share.

[2] On a reverse split adjusted basis the number of shares repurchased was 10.3 million for $47.42 per share.