Shareholders' Equity - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013
Stockholders Equity Disclosure [Abstract]
Stock repurchase program authorized amount	$ 426
After tax gain on sale of subsidiary	$ 198	$ 92
Common shares dividend per share quarterly	$ 0.055