Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 BusinessTaxProvision	Sep. 30, 2012	Dec. 31, 2012
Income Taxes [Line Items]
Effective tax rate	41.30%	15.90%	63.70%	25.10%
U.S federal statutory rate	35.00%	35.00%	35.00%
Operational losses in certain foreign jurisdictions	$ 6	$ 35		$ 39
Gain from the sale of the Tapoco Hydroelectric Project		12		12
Nondeductible charge			103
Number of specific temporary business tax provisions expired during the period			2
Tax provision due to two specific temporary business tax provision that expired in 2011					19
Discrete income tax charge				8
Minimum [Member]
Income Taxes [Line Items]
U.S federal statutory rate				35.00%
Maximum [Member]
Income Taxes [Line Items]
U.S federal statutory rate				(60.10%)
Spain and Australia Authority [Member]
Income Taxes [Line Items]
Discrete income tax benefit			10
U.S. [Member]
Income Taxes [Line Items]
Discrete income tax benefit			$ 19