Schedule of Interest Income and Interest Expense (Parenthetical) (Detail) (Variable Interest Entity, Not Primary Beneficiary, USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Variable Interest Entity, Not Primary Beneficiary
Amounts Related To Interest [Line Items]
Interest expense and interest income excluded, amount	$ 12	$ 12	$ 20	$ 26