Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

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The total charge for the use of long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment
Property and equipment, gross	$ 24,290	$ 22,802
Accumulated depreciation and amortization	(13,998)	(12,627)
Property and equipment, net	10,292	10,175
Property and equipment under capital leases	588	547
Capital leases, accumulated depreciation	140	119
Depreciation expense	1,700	1,700	$ 1,500
Land
Property, Plant and Equipment
Property and equipment, gross	1,707	1,734
Furniture and Fixtures
Property, Plant and Equipment
Property and equipment, gross	11,963	10,956
Leasehold Improvements
Property, Plant and Equipment
Property and equipment, gross	4,793	4,494
Building and Building Improvements
Property, Plant and Equipment
Property and equipment, gross	3,343	3,226
Software
Property, Plant and Equipment
Property and equipment, gross	$ 2,484	$ 2,392
Minimum \| Building
Property, Plant and Equipment
Estimated useful life (in years)	10 years
Minimum \| Building Improvements
Property, Plant and Equipment
Estimated useful life (in years)	10 years
Minimum \| Furniture and Fixtures
Property, Plant and Equipment
Estimated useful life (in years)	3 years
Minimum \| Leasehold Improvements
Property, Plant and Equipment
Estimated useful life (in years)	10 years
Minimum \| Equipment
Property, Plant and Equipment
Estimated useful life (in years)	3 years
Minimum \| Software and Software Development Costs
Property, Plant and Equipment
Estimated useful life (in years)	3 years
Maximum \| Building
Property, Plant and Equipment
Estimated useful life (in years)	40 years
Maximum \| Building Improvements
Property, Plant and Equipment
Estimated useful life (in years)	40 years
Maximum \| Furniture and Fixtures
Property, Plant and Equipment
Estimated useful life (in years)	10 years
Maximum \| Leasehold Improvements
Property, Plant and Equipment
Estimated useful life (in years)	40 years
Maximum \| Equipment
Property, Plant and Equipment
Estimated useful life (in years)	10 years
Maximum \| Software and Software Development Costs
Property, Plant and Equipment
Estimated useful life (in years)	10 years