Derivative Financial Instruments - Notional Values of Derivative Contracts (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Total	$ 7,074	$ 8,933
Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Total	0	1,859
Currency swaps [Member]
Derivatives, Fair Value [Line Items]
Total	1,562	1,562
Debt Option [Member]
Derivatives, Fair Value [Line Items]
Total	1,562	3,421
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Total	2,888	2,888
Derivatives designated as hedging instruments [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Total	1,300	1,300
Derivatives designated as hedging instruments [Member] | Currency swaps [Member]
Derivatives, Fair Value [Line Items]
Total	1,588	1,588
Derivatives not designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Total	2,624	2,624
Derivatives not designated as hedging instruments [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Total	$ 2,624	$ 2,624