Natural Gas And Oil Producing Activities (Unaudited) (Capitalized Costs Relating To Oil And Gas Producing Activities Disclosure) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Proved properties	$ 15,860	$ 12,337
Unproved properties	4,646	957
Total capitalized costs	20,506	13,294
Less: Accumulated depreciation, depletion and amortization	8,327	7,481
Net capitalized costs	12,179	5,813
Unproved property acquisition costs	3,934	168	221
Capitalized costs incurred	7,221	2,023	1,911
Capitalized Costs [Member] | Exploration Program in Canada [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Unproved property acquisition costs	76	72
Chesapeake Property Acquisition [Member] | Capitalized Costs [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Capitalized costs incurred	$ 5,000