Income Taxes - Net Operating Losses (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
United States [Member]
Net operating losses:
Net operating losses	$ 2,393
Net operating losses, Expiration	2027
United States State [Member]
Net operating losses:
Net operating losses	1,648
Net operating losses, Expiration	Various
Canada [Member]
Net operating losses:
Net operating losses	6
Net operating losses, Expiration	2014
Australia [Member]
Net operating losses:
Net operating losses	94
Net operating losses, Expiration	Indefinite
Argentina [Member]
Net operating losses:
Net operating losses	$ 55
Net operating losses, Expiration	2013