Guarantor Condensed Consolidated Financial Statements - Schedule of Guarantor Subsidiaries Condensed Consolidating Balance Sheets (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Assets
Cash and cash equivalents	$ 1,389	$ 716	$ 186	$ 154
Investment in subsidiaries
Other current assets	1,265	1,457
Property, plant and equipment, net	1,309	1,423
Mineral leaseholds, net	1,321	1,439
Other assets	80	59
Total Assets	5,847	5,511
Liabilities and Shareholders' Equity
Current liabilities	336	467
Long-term debt	2,390	1,605
Other long-term liabilities	49	53
Total Liabilities	3,257	2,629
Total Shareholders' Equity	2,384	2,649
Total Liabilities and Equity	5,847	5,511
Eliminations [Member]
Assets
Cash and cash equivalents
Investment in subsidiaries	(1,132)	(1,595)
Other current assets	(9,173)	(8,300)
Total Assets	(10,305)	(9,895)
Liabilities and Shareholders' Equity
Current liabilities	(1,155)	(539)
Other long-term liabilities	(7,947)	(7,709)
Total Liabilities	(9,102)	(8,248)
Total Shareholders' Equity	(1,203)	(1,647)
Total Liabilities and Equity	(10,305)	(9,895)
Parent Company [Member]
Assets
Cash and cash equivalents	398	533
Investment in subsidiaries	(878)	(622)
Other current assets	6,285	6,047
Other assets	(3)	(3)
Total Assets	5,802	5,955
Liabilities and Shareholders' Equity
Current liabilities	473	560
Other long-term liabilities	933	882
Total Liabilities	1,406	1,442
Total Shareholders' Equity	4,396	4,513
Total Liabilities and Equity	5,802	5,955
Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	882	82	143	107
Investment in subsidiaries	1,553	1,760
Other current assets	2,048	2,181
Property, plant and equipment, net	729	747
Mineral leaseholds, net	766	796
Other assets	382	401
Total Assets	6,360	5,967
Liabilities and Shareholders' Equity
Current liabilities	842	133
Long-term debt	901	902
Other long-term liabilities	7,136	6,978
Total Liabilities	8,879	8,013
Total Shareholders' Equity	(2,519)	(2,046)
Total Liabilities and Equity	6,360	5,967
Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents	109	101	43	47
Investment in subsidiaries	457	457
Other current assets	2,105	1,529
Property, plant and equipment, net	580	676
Mineral leaseholds, net	555	643
Other assets	184	78
Total Assets	3,990	3,484
Liabilities and Shareholders' Equity
Current liabilities	176	313
Long-term debt	1,489	703
Other long-term liabilities	409	406
Total Liabilities	2,074	1,422
Total Shareholders' Equity	1,916	2,062
Total Liabilities and Equity	$ 3,990	$ 3,484