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	Dec. 31, 2018	Dec. 31, 2017
Offsetting [Abstract]
Cash collateral netted against derivative liabilities	$ 240	$ 528
Derivative liabilities not subject to netting arrangements	$ 85	$ 738

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

Dec. 31, 2018

Dec. 31, 2017

Cash collateral netted against derivative liabilities

$ 240

$ 528

Derivative liabilities not subject to netting arrangements

$ 85

$ 738