Shareholder's Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended
	Jun. 14, 2007	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shareholders Equity [Line Items]
Common shares, authorized		200,000,000
Common shares, par value		$ 1	$ 1
Preference shares, authorized		500,000
Repurchase of outstanding common stock, authorized amount	$ 300
Weighted average antidilutive which were not included in the calculation of earnings per share		9,041,000	8,825,000	4,391,000