Supplemental Information On Oil And Gas Operations (Standardized Measure Of Discounted Future Net Cash Flows Related To Interest In Proved Reserves) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	$ 32,519	$ 40,445	$ 107,218
Future costs:
Development	(4,985)	(6,065)	(10,787)
Production	(20,771)	(24,142)	(43,972)
Future income tax expense	(57)	(475)	(14,047)
Future net cash flow	6,706	9,763	38,412
10% discount to reflect timing of cash flows	(2,508)	(3,075)	(17,938)
Standardized measure of discounted future net cash flows	4,198	6,688	20,474	$ 15,741
United States [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	22,847	27,398	75,847
Future costs:
Development	(2,784)	(3,306)	(7,168)
Production	(14,484)	(17,251)	(29,740)
Future income tax expense			(11,021)
Future net cash flow	5,579	6,841	27,918
10% discount to reflect timing of cash flows	(2,128)	(1,973)	(12,819)
Standardized measure of discounted future net cash flows	3,451	4,868	15,099
Canada [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	9,672	13,047	31,371
Future costs:
Development	(2,201)	(2,759)	(3,619)
Production	(6,287)	(6,891)	(14,232)
Future income tax expense	(57)	(475)	(3,026)
Future net cash flow	1,127	2,922	10,494
10% discount to reflect timing of cash flows	(380)	(1,102)	(5,119)
Standardized measure of discounted future net cash flows	$ 747	$ 1,820	$ 5,375