Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt carried at fair value	$ (8,034)		$ (9,725)
Derivative related liabilities	(1)		(22)
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
Long-term debt carried at fair value	0		0
Derivative related liabilities	0		0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to affiliates carried at fair value	(493)		(514)
Long-term debt carried at fair value	(8,034)		(9,725)
Derivative related liabilities	(1)		(22)
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
Long-term debt carried at fair value	0		0
Derivative related liabilities	0		0
Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Available-for-sale securities			80
Total assets	0		80
Due to affiliates carried at fair value	0		0
Long-term debt carried at fair value	0		0
Derivative related liabilities	0		0
Total liabilities	0		0
Recurring [Member] | Level 1 [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities			80
Recurring [Member] | 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] | 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] | 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] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	1,281		1,683
Available-for-sale securities			0
Total assets	1,281		1,683
Due to affiliates carried at fair value	(493)		(514)
Long-term debt carried at fair value	(8,034)		(9,725)
Derivative related liabilities	(480)		(1,630)
Total liabilities	(9,007)		(11,869)
Recurring [Member] | Level 2 [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities			0
Recurring [Member] | Level 2 [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	353		524
Derivative related liabilities	(421)		(1,585)
Recurring [Member] | Level 2 [Member] | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	928		1,159
Derivative related liabilities	(59)		(45)
Recurring [Member] | 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] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Available-for-sale securities			0
Total assets	0		0
Due to affiliates carried at fair value	0		0
Long-term debt carried at fair value	0		0
Derivative related liabilities	0		0
Total liabilities	0		0
Recurring [Member] | Level 3 [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities			0
Recurring [Member] | 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] | 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] | 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] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	(1,281)	[1]	(1,683)	[1]
Available-for-sale securities			0	[1]
Total assets	(1,281)	[1]	(1,683)	[1]
Due to affiliates carried at fair value	0	[1]	0	[1]
Long-term debt carried at fair value	0	[1]	0	[1]
Derivative related liabilities	479	[1]	1,608	[1]
Total liabilities	479	[1]	1,608	[1]
Recurring [Member] | Netting [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities			0	[1]
Recurring [Member] | 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] | 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] | Netting [Member] | Derivative netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	(1,281)	[1]	(1,683)	[1]
Derivative related liabilities	479	[1]	1,608	[1]
Recurring [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	0		0
Available-for-sale securities			80
Total assets	0		80
Due to affiliates carried at fair value	(493)		(514)
Long-term debt carried at fair value	(8,034)		(9,725)
Derivative related liabilities	(1)		(22)
Total liabilities	(8,528)		(10,261)
Recurring [Member] | Fair Value [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities			80
Recurring [Member] | Fair Value [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	353		524
Derivative related liabilities	(421)		(1,585)
Recurring [Member] | Fair Value [Member] | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	928		1,159
Derivative related liabilities	(59)		(45)
Recurring [Member] | Fair Value [Member] | Derivative netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	(1,281)		(1,683)
Derivative related liabilities	$ 479		$ 1,608

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