Fair Value Measurements (Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs) (Level 3) (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Derivative assets	$ 400	$ 412	$ 380	$ 761	$ 633	$ 484
Interest Rates
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Derivative assets	33			19
Derivative liabilities	4			3
Equity Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Derivative assets	325			630
Derivative liabilities	$ 103			$ 58