Significant Accounting Policies - Property Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 31,306.0	$ 28,934.0
Accumulated depreciation and amortization	(18,700.0)	(16,890.0)
Property and equipment, net	12,606.0	12,044.0
Land
Property, Plant and Equipment [Line Items]
Total property and equipment	2,134.0	1,981.0
Building and improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	3,950.0	3,541.0
Fixtures and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	13,125.0	12,401.0
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	6,077.0	5,611.0
Software
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 6,020.0	$ 5,400.0