Netting Arrangements for Certain Financial Instruments - Information on Company's Accounting Netting Adjustments and Items Not Offset in Consolidated Balance Sheet But Available for Offset in Event of Default (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Offsetting [Abstract]
Cash collateral netted against derivative assets	$ 75	$ 79
Derivative assets not subject to netting arrangements	183	260
Cash collateral netted against derivative liabilities	862	1,200
Derivative liabilities not subject to netting arrangements	$ 55	$ 5