Netting Arrangements for Certain Financial Instruments and Securities Financing Activities - 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	Mar. 31, 2015	Dec. 31, 2014
Offsetting [Abstract]
Cash collateral netted against derivative assets	$ 292	$ 258
Derivative assets not subject to netting arrangements	428	221
Cash collateral netted against derivative liabilities	727	705
Derivative liabilities not subject to netting arrangements	$ 522	$ 342