Derivative Financial Instruments - Notional Values of Derivative Contracts (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Total	$ 8,933	$ 13,980
Debt option [Member]
Derivatives, Fair Value [Line Items]
Total	3,421	6,574
Interest rate swaps [Member] | Debt option [Member]
Derivatives, Fair Value [Line Items]
Total	1,859	3,682
Currency swaps [Member] | Debt option [Member]
Derivatives, Fair Value [Line Items]
Total	1,562	2,892
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Total	2,888	4,207
Derivatives designated as hedging instruments [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Total	1,300	1,959
Derivatives designated as hedging instruments [Member] | Currency swaps [Member]
Derivatives, Fair Value [Line Items]
Total	1,588	2,248
Derivatives not designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Total	2,624	3,199
Derivatives not designated as hedging instruments [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Total	$ 2,624	$ 3,199