Leases (Supplemental Balance Sheet Information Related to Leases) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Operating Lease [Abstract]
Operating Lease, Right-of-Use Asset	$ 24,477	$ 0
Accounts payable and accrued liabilities	43,955	43,184
Operating lease liabilities	22,288	0
Total	25,741
Finance Lease [Abstract]
Property, plant and equipment, at cost	337,240	330,690
Accumulated depreciation and amortization	(205,924)	(199,217)
Property, plant and equipment - net	131,316	$ 131,473
Current portion of long-term debt	153
Long-term debt	1,823
Total finance lease obligation	$ 1,976
Operating Lease, Weighted Average Remaining Lease Term	8 years 8 months 12 days
Finance Lease, Weighted Average Remaining Lease Term	10 years 4 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	4.30%
Finance Lease, Weighted Average Discount Rate, Percent	8.40%
Operating Lease
Operating Lease [Abstract]
Accounts payable and accrued liabilities	$ 3,453
Finance Lease
Finance Lease [Abstract]
Property, plant and equipment, at cost	3,438
Accumulated depreciation and amortization	(1,215)
Property, plant and equipment - net	$ 2,223