Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative related liabilities	$ (101)		$ (82)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to affiliates carried at fair value	0		0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to affiliates carried at fair value	(513)		(512)
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to affiliates carried at fair value	0		0
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Due to affiliates carried at fair value	0		0
Derivative related liabilities	0		0
Total liabilities	0		0
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Derivative related liabilities	0		0
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Derivative related liabilities	0		0
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Derivative netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Derivative related liabilities	0		0
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	233		291
Due to affiliates carried at fair value	(513)		(512)
Derivative related liabilities	(1,062)		(586)
Total liabilities	(7,971)		(7,860)
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	106		144
Derivative related liabilities	(511)		(453)
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	127		147
Derivative related liabilities	(551)		(133)
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Derivative netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Derivative related liabilities	0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Due to affiliates carried at fair value	0		0
Derivative related liabilities	0		0
Total liabilities	0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Derivative related liabilities	0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Derivative related liabilities	0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Derivative netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Derivative related liabilities	0		0
Recurring [Member] | Derivatives, Fair Value, Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	(233)	[1]	(291)	[1]
Due to affiliates carried at fair value	0	[1]	0	[1]
Derivative related liabilities	961	[1]	504	[1]
Total liabilities	961	[1]	504	[1]
Recurring [Member] | Derivatives, Fair Value, Netting [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0	[1]	0	[1]
Derivative related liabilities	0	[1]	0	[1]
Recurring [Member] | Derivatives, Fair Value, Netting [Member] | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0	[1]	0	[1]
Derivative related liabilities	0	[1]	0	[1]
Recurring [Member] | Derivatives, Fair Value, Netting [Member] | Derivative netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	(233)	[1]	(291)	[1]
Derivative related liabilities	961	[1]	504	[1]
Long-term Debt Carried at Fair Value [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term debt	0		0
Long-term Debt Carried at Fair Value [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term debt	(6,396)		(6,762)
Long-term Debt Carried at Fair Value [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term debt	0		0
Long-term Debt Carried at Fair Value [Member] | Recurring [Member] | Derivatives, Fair Value, Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term debt	0	[1]	0	[1]
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to affiliates carried at fair value	(513)		(512)
Fair Value [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Due to affiliates carried at fair value	(513)		(512)
Derivative related liabilities	(101)		(82)
Total liabilities	(7,010)		(7,356)
Fair Value [Member] | Recurring [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	106		144
Derivative related liabilities	(511)		(453)
Fair Value [Member] | Recurring [Member] | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	127		147
Derivative related liabilities	(551)		(133)
Fair Value [Member] | Recurring [Member] | Derivative netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	(233)		(291)
Derivative related liabilities	961		504
Fair Value [Member] | Long-term Debt Carried at Fair Value [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term debt	$ (6,396)		$ (6,762)

[1] Represents counterparty and swap collateral netting which allow the offsetting of amounts relating to certain contracts when certain conditions are met.