Acquisitions and Divestitures - Summary of Carrying Amount of Major Assets and Liabilities Associated with Disposition - Australia Divestitures (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
ASSETS
Current assets	$ 4,079	$ 6,415
Total assets	27,812	55,952	$ 52,340
LIABILITIES
Current liabilities	2,167	3,664
Asset retirement obligations	2,567	3,048
Non-current deferred tax liability	1,997	9,499
Other long-term liabilities	$ 332	359
Divestiture [Member] | Australia [Member]
ASSETS
Current assets		1,992
Net property and equipment		6,516
Total assets		8,508
LIABILITIES
Current liabilities		606
Asset retirement obligations		517
Non-current deferred tax liability		922
Other long-term liabilities		33
Total liabilities		$ 2,078