Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	$ 131		$ 0
Long-term debt carried at fair value	(9,600)		(9,700)
Derivative related liabilities	(1)		(22)
Level 1
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
Long-term debt carried at fair value	0		0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	131		0
Due to affiliates carried at fair value	(511)		(514)
Long-term debt carried at fair value	(9,573)		(9,725)
Level 3
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
Long-term debt carried at fair value	0		0
Recurring [Member] | Level 1
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 | 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 | 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 | 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 | 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
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	1,310		1,683
Available-for-sale securities			0
Total assets	1,310		1,683
Due to affiliates carried at fair value	(511)		(514)
Long-term debt carried at fair value	(9,573)		(9,725)
Derivative related liabilities	(833)		(1,630)
Total liabilities	(10,917)		(11,869)
Recurring [Member] | Level 2 | 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 | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	455		524
Derivative related liabilities	(709)		(1,585)
Recurring [Member] | Level 2 | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	855		1,159
Derivative related liabilities	(124)		(45)
Recurring [Member] | Level 2 | 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
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 | 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 | 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 | 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 | 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	(1,179)	[1]	(1,683)	[1]
Available-for-sale securities			0	[1]
Total assets	(1,179)	[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	832	[1]	1,608	[1]
Total liabilities	832	[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	(1,179)	[1]	(1,683)	[1]
Derivative related liabilities	(832)	[1]	1,608	[1]
Recurring [Member] | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	131		0
Available-for-sale securities			80
Total assets	131		80
Due to affiliates carried at fair value	(511)		(514)
Long-term debt carried at fair value	(9,573)		(9,725)
Derivative related liabilities	(1)		(22)
Total liabilities	(10,085)		(10,261)
Recurring [Member] | Fair Value | 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 | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	455		524
Derivative related liabilities	(709)		(1,585)
Recurring [Member] | Fair Value | Currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	855		1,159
Derivative related liabilities	(124)		(45)
Recurring [Member] | Fair Value | Derivative netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets	(1,179)		(1,683)
Derivative related liabilities	$ (832)		$ 1,608

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