Dispositions (Details) - USD ($) $ in Millions	1 Months Ended						2 Months Ended	3 Months Ended		12 Months Ended
	Nov. 30, 2015	Aug. 31, 2015	Jun. 30, 2014	Jun. 30, 2013	Feb. 28, 2013	Jan. 31, 2013	Feb. 22, 2016	Mar. 31, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2015
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment										$ 225	$ 3,760	$ 450
GOM Producing Properties [Member]
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment	$ 111	$ 228
Kenya and Ethiopia Assets [Member]
Dispositions Detail [Line Items]
Pretax gain/loss on sale													$ 109
East Texas/North Louisiana and Wilburton Assets [Member]
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment		$ 100
Pretax gain/loss on sale													$ 1
Williston Basin [Member]
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment			$ 90
Pretax gain/loss on sale			$ 91
DJ Basin [Member]
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment				$ 19
Pretax gain/loss on sale				114
Marcellus Shale [Member]
Dispositions Detail [Line Items]
Pretax gain/loss on sale					$ 43
Neptune Gas Plant [Member]
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment					166
Pretax gain/loss on sale					$ (98)
Alaska EP [Member]
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment						$ 195
Proceeds from Sale of Oil and Gas Property and Equipment, Six Month Escrow						$ 50
Pretax gain/loss on sale				$ (55)
Safen Block [Member]
Dispositions Detail [Line Items]
Pretax gain/loss on sale												$ 17
Interest Percentage												45.00%
Neptune Field [Member]
Dispositions Detail [Line Items]
Disposal Group, Including Discontinued Operation, Assets										31
Disposal Group, Including Discontinued Operation, Liabilities										54
Fair Value, Measurements, Nonrecurring [Member]
Dispositions Detail [Line Items]
Assets, Fair Value Adjustment										$ 412	$ 132	$ 96
Fair Value, Measurements, Nonrecurring [Member] | East Texas/North Louisiana and Wilburton Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Dispositions Detail [Line Items]
Assets, Fair Value Adjustment									$ (44)
Subsequent Event [Member] | Neptune Field [Member]
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment							$ 4
Scenario, Forecast [Member] | Kenya and Ethiopia Assets [Member]
Dispositions Detail [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment								$ (10)