Leases (Supplemental Balance Sheet Information Related to Leases) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Operating Lease [Abstract]
Operating Lease, Right-of-Use Asset	$ 20,235	$ 0
Accounts payable and accrued liabilities	42,306	43,184
Operating lease liabilities	18,253	0
Total	21,325
Finance Lease [Abstract]
Property, plant and equipment, at cost	332,517	330,690
Accumulated depreciation and amortization	(200,466)	(199,217)
Property, plant and equipment - net	132,051	$ 131,473
Current portion of long-term debt	135
Long-term debt	1,852
Total finance lease obligation	$ 1,987
Operating Lease, Weighted Average Discount Rate, Percent	4.70%
Finance Lease, Weighted Average Discount Rate, Percent	8.60%
Operating Lease
Operating Lease [Abstract]
Accounts payable and accrued liabilities	$ 3,072
Finance Lease
Finance Lease [Abstract]
Property, plant and equipment, at cost	3,377
Accumulated depreciation and amortization	(1,173)
Property, plant and equipment - net	$ 2,204