Supplemental Oil and Gas Disclosures - Summary of Oil and Gas Property Costs Not Being Amortized (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs	$ 5,013
Exploration and development	1,777
Capitalized interest	224
Costs incurred	7,014
2014 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs	1,770
Exploration and development	1,285
Capitalized interest	43
Costs incurred	3,098
2013 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs	242
Exploration and development	402
Capitalized interest	43
Costs incurred	687
2012 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs	2,079
Exploration and development	65
Capitalized interest	47
Costs incurred	2,191
2011 and Prior [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs	922
Exploration and development	25
Capitalized interest	91
Costs incurred	$ 1,038