Stockholders Equity - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended			3 Months Ended	9 Months Ended
	Sep. 30, 2013	Feb. 28, 2013 Maximum	Feb. 28, 2013 Accelerated Share Repurchase Program	Sep. 30, 2013 Accelerated Share Repurchase Program	Sep. 30, 2013 Accelerated Share Repurchase Program
Stockholders' Equity [Line Items]
Shares issued in equity offering	16.5
Price per share received in equity offering	$ 47.00
Proceeds from issuance of common stock, net	$ 745
Repurchase of common stock, authorized value		500	250
Stock repurchase, amount paid					250
Stock repurchase, shares delivered				0.1	5.6
Stock repurchase, amount recorded as treasury stock					$ 250