Natural Gas And Oil Producing Activities (Unaudited) (Cost Incurred In Oil And Gas Property Acquisition, Exploration, And Development Activities Disclosure) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Proved property acquisition costs	$ 1,455	$ 1
Unproved property acquisition costs	3,934	168	221
Exploration costs	232	192	197
Development costs	1,600	1,662	1,493
Capitalized costs incurred	7,221	2,023	1,911
Full cost pool amortization per Mcfe	1.10	1.08	1.31
Costs Incurred in Natural Gas and Oil Exploration and Development [Member] | Exploration Program in Canada [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Unproved property acquisition costs	1	17	4
Exploration costs	$ 3	$ 12	$ 3