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 Liabilities But Available for Offset in Event of Default (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Offsetting [Abstract]
Cash collateral netted against derivative liabilities	$ 533	$ 411
Derivative liabilities not subject to netting arrangements	$ 768	$ 908

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 Liabilities But Available for Offset in Event of Default (Parenthetical) (Detail) - USD ($)
$ in Millions

Sep. 30, 2017

Dec. 31, 2016

Cash collateral netted against derivative liabilities

$ 533

$ 411

Derivative liabilities not subject to netting arrangements

$ 768

$ 908