Debt - Long-term debt (Detail) (USD $) In Millions, unless otherwise specified					12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012	Feb. 14, 2011	Dec. 31, 2012 Successor [Member]	Dec. 31, 2011 Successor [Member]	Dec. 31, 2012 Term Facility [Member]	Dec. 31, 2012 Term Facility [Member] Successor [Member]	Dec. 31, 2012 Secured Bonds [Member]	Dec. 31, 2012 Secured Bonds [Member] Successor [Member]	Dec. 31, 2012 Exit Financing Facility [Member]	Dec. 31, 2011 Exit Financing Facility [Member] Successor [Member]	Dec. 31, 2012 Co-generation Unit Financing Arrangement [Member]	Dec. 31, 2012 Co-generation Unit Financing Arrangement [Member] Successor [Member]	Dec. 31, 2011 Co-generation Unit Financing Arrangement [Member] Successor [Member]
Long Term Debt Current And Noncurrent [Line Items]
Co-generation Unit Financing Arrangement	$ 1,615		$ 1,615	$ 427		$ 691		$ 900		$ 421		$ 10	$ 6
Lease financing			14
Less: Long-term debt due in one year			(10)	(6)
Long-term debt			1,605	421
Maturity Date					Feb. 08, 2018		Aug. 15, 2020		Oct. 21, 2015		Feb. 01, 2016
Initial Principal Amount		$ 425			$ 700	$ 697	$ 900		$ 425		$ 16