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, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative assets	$ 761	$ 484	$ 422	$ 437
Interest Rates
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative assets	19		10
Derivative liabilities	3		3
Equity Contract
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative assets	630		358
Derivative liabilities	$ 58		$ 53