Supplemental Information On Oil And Gas Operations (Oil And Gas Properties Not Subject To Amortization) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition costs	$ 2,465
Exploration costs	536
Development costs	185
Capitalized interest	251
Total oil and gas properties not subject to amortization	3,437
2016 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition costs	1,176
Exploration costs	107
Development costs	12
Capitalized interest	63
Total oil and gas properties not subject to amortization	1,358
2015 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition costs	579
Exploration costs	134
Capitalized interest	52
Total oil and gas properties not subject to amortization	765
2014 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition costs	246
Exploration costs	89
Development costs	23
Capitalized interest	37
Total oil and gas properties not subject to amortization	395
Prior to 2014 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition costs	464
Exploration costs	206
Development costs	150
Capitalized interest	99
Total oil and gas properties not subject to amortization	$ 919