Capital Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		12 Months Ended
	Sep. 21, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2011
Capital Stock [Line Items]
Common stock, shares authorized			1,800,000,000		1,800,000,000
Initial public offering of shares common stock		87,719,300
Initial public offering of shares of common stock, price per share		$ 30.00
Proceeds from issuance of initial public offering		$ 2,506
Repurchase of common stock	80,771,143
Repurchase of common stock, per share	$ 18.61
Shares repurchased as percentage of total shares outstanding	15.60%
Value of distribution per share			$ 6.50	$ 9.43
Value of distribution			$ 3,142	$ 4,332
Reduction of non vested stock options on exercise price of share-based awards			$ 6.50	$ 9.43
Minimum [Member]
Capital Stock [Line Items]
Number of directors as per the amended and restated by-laws			3