Fair Value Option - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Disclosure Fair Value Option Additional Information [Abstract]
Fixed rate debt accounted for under fair value option	$ 10,200,000,000	$ 14,100,000,000
Long-term debt carried at fair value	9,700,000,000	13,700,000,000
Due To Affiliate Carried At Fair Value	514,000,000	447,000,000
Fair value option not elected related to fixed rate long-term debt	8,100,000,000	11,800,000,000
Aggregate unpaid principal balance of fixed rate debt accounted for under fair value option	9,400,000,000	13,900,000,000
Increased the debt balance	247,000,000	341,000,000
Cumulative increased value of debt through fair value option adjustments	$ 824,000,000	$ 232,000,000