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 Assets But Available for Offset in Event of Default (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Offsetting [Abstract]
Cash collateral netted against derivative assets	$ 152	$ 165
Derivative assets not subject to netting arrangements	$ 1,300	$ 368

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

Sep. 30, 2016

Dec. 31, 2015

Cash collateral netted against derivative assets

$ 152

$ 165

Derivative assets not subject to netting arrangements

$ 1,300

$ 368