Capital Stock - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Jul. 30, 2007	Feb. 12, 2013 Subsequent event	Dec. 31, 2012 Common Stock	Dec. 31, 2011 Common Stock	Dec. 31, 2012 Series common stock	Dec. 31, 2011 Series common stock
Schedule Of Capital Stock [Line Items]
All classes of stock, shares authorized	1,020,000,000
Shares of all classes of stock, par value	$ 0.01
Common stock, shares authorized					1,000,000,000	1,000,000,000	10,000,000	10,000,000
Preferred stock, shares authorized	10,000,000	10,000,000
Shares authorized to be repurchased			2,000,000,000	1,000,000,000
Shares repurchased during the period	4,800,000
Shares issued during the period for stock-based compensation plans	6,000,000
Dividends declared per share	$ 0.20
Dividends declaration date	Dec. 11, 2012
Dividends payable date	Mar. 11, 2013
Dividends payable record date	Feb. 20, 2013