Supplementary Information - Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 1	$ 2	$ 33	$ 25
Accounts receivable, net	136	154
Inventories	37	43
Other	49	107
Total current assets	223	306
Property, plant and equipment, net	3,446	3,476
Goodwill and intangible assets, net	182	184
Advances receivable - consolidated subsidiaries	0	0
Investments in consolidated subsidiaries	0	0
Investments in unconsolidated affiliates	1,486	1,493
Other long-term assets	17	18
Total assets	5,354	5,477
LIABILITIES AND EQUITY
Accounts payable and other current liabilities	175	200
Advances payable - consolidated subsidiaries	0	0
Long-term debt	2,377	2,424
Other long-term liabilities	48	48
Total liabilities	$ 2,600	$ 2,672
Commitments and contingent liabilities
Equity:
Net equity	$ 2,731	$ 2,780
Accumulated other comprehensive loss	(8)	(8)
Total partners' equity	2,723	2,772
Noncontrolling interests	31	33
Total equity	2,754	2,805	3,006	3,026
Total liabilities and equity	5,354	5,477
Parent Guarantor [Member]
ASSETS
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Inventories	0	0
Other	0	0
Total current assets	0	0
Property, plant and equipment, net	0	0
Goodwill and intangible assets, net	0	0
Advances receivable - consolidated subsidiaries	2,038	2,159
Investments in consolidated subsidiaries	685	613
Investments in unconsolidated affiliates	0	0
Other long-term assets	0	0
Total assets	2,723	2,772
LIABILITIES AND EQUITY
Accounts payable and other current liabilities	0	0
Advances payable - consolidated subsidiaries	0	0
Long-term debt	0	0
Other long-term liabilities	0	0
Total liabilities	$ 0	$ 0
Commitments and contingent liabilities
Equity:
Net equity	$ 2,723	$ 2,772
Accumulated other comprehensive loss	0	0
Total partners' equity	2,723	2,772
Noncontrolling interests	0	0
Total equity	2,723	2,772
Total liabilities and equity	2,723	2,772
Subsidiary Issuer [Member]
ASSETS
Cash and cash equivalents	0	0	32	24
Accounts receivable, net	0	0
Inventories	0	0
Other	0	0
Total current assets	0	0
Property, plant and equipment, net	0	0
Goodwill and intangible assets, net	0	0
Advances receivable - consolidated subsidiaries	1,963	2,023
Investments in consolidated subsidiaries	1,129	1,033
Investments in unconsolidated affiliates	0	0
Other long-term assets	0	0
Total assets	3,092	3,056
LIABILITIES AND EQUITY
Accounts payable and other current liabilities	30	19
Advances payable - consolidated subsidiaries	0	0
Long-term debt	2,377	2,424
Other long-term liabilities	0	0
Total liabilities	$ 2,407	$ 2,443
Commitments and contingent liabilities
Equity:
Net equity	$ 688	$ 616
Accumulated other comprehensive loss	(3)	(3)
Total partners' equity	685	613
Noncontrolling interests	0	0
Total equity	685	613
Total liabilities and equity	3,092	3,056
Non-Guarantor Subsidiaries [Member]
ASSETS
Cash and cash equivalents	1	2	1	1
Accounts receivable, net	136	154
Inventories	37	43
Other	49	107
Total current assets	223	306
Property, plant and equipment, net	3,446	3,476
Goodwill and intangible assets, net	182	184
Advances receivable - consolidated subsidiaries	0	0
Investments in consolidated subsidiaries	0	0
Investments in unconsolidated affiliates	1,486	1,493
Other long-term assets	17	18
Total assets	5,354	5,477
LIABILITIES AND EQUITY
Accounts payable and other current liabilities	145	181
Advances payable - consolidated subsidiaries	4,001	4,182
Long-term debt	0	0
Other long-term liabilities	48	48
Total liabilities	$ 4,194	$ 4,411
Commitments and contingent liabilities
Equity:
Net equity	$ 1,134	$ 1,038
Accumulated other comprehensive loss	(5)	(5)
Total partners' equity	1,129	1,033
Noncontrolling interests	31	33
Total equity	1,160	1,066
Total liabilities and equity	5,354	5,477
Consolidating Adjustments [Member]
ASSETS
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts receivable, net	0	0
Inventories	0	0
Other	0	0
Total current assets	0	0
Property, plant and equipment, net	0	0
Goodwill and intangible assets, net	0	0
Advances receivable - consolidated subsidiaries	(4,001)	(4,182)
Investments in consolidated subsidiaries	(1,814)	(1,646)
Investments in unconsolidated affiliates	0	0
Other long-term assets	0	0
Total assets	(5,815)	(5,828)
LIABILITIES AND EQUITY
Accounts payable and other current liabilities	0	0
Advances payable - consolidated subsidiaries	(4,001)	(4,182)
Long-term debt	0	0
Other long-term liabilities	0	0
Total liabilities	$ (4,001)	$ (4,182)
Commitments and contingent liabilities
Equity:
Net equity	$ (1,814)	$ (1,646)
Accumulated other comprehensive loss	0	0
Total partners' equity	(1,814)	(1,646)
Noncontrolling interests	0	0
Total equity	(1,814)	(1,646)
Total liabilities and equity	$ (5,815)	$ (5,828)