Fair Value Measurements - Debt Excluding Capital Leases (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument fair value	$ 111,631	$ 110,373
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument fair value	137,420	129,200
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument fair value	89,504	86,712
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument fair value	47,916	42,488
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument fair value	$ 0	$ 0