Commitments and Contingencies - Contractual Obligations (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Oil and Gas Delivery Commitments and Contracts [Line Items]
Total	$ 5,403
2013	2,208
2014-2015	2,142
2016-2017	622
2018 & Beyond	431
Drilling Rig Commitments [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Total	896
2013	602
2014-2015	289
2016-2017	3
2018 & Beyond	2
Purchase Obligations [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Total	2,588
2013	1,200
2014-2015	1,182
2016-2017	184
2018 & Beyond	22
Firm Transportation Agreements [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Total	763
2013	148
2014-2015	264
2016-2017	134
2018 & Beyond	217
Office Equipment [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Total	402
2013	49
2014-2015	91
2016-2017	96
2018 & Beyond	166
Other Contractual Obligation [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Total	754
2013	209
2014-2015	316
2016-2017	205
2018 & Beyond	$ 24