Summary of Significant Accounting Policies - Narrative (Details) - USD ($)
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12 Months Ended |
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Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Jan. 01, 2019 |
| Summary of Significant Accounting Policies [Line Items] |
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| Voting rights threshold for consolidation |
50.00%
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| Stranded tax effects in AOCI elected not to reclassify |
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$ 1,200,000,000
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| Depreciation and amortization expense related to property and equipment |
$ 2,581,000,000
|
$ 2,329,000,000
|
$ 2,222,000,000
|
|
| Amortization of capitalized software |
239,000,000
|
205,000,000
|
187,000,000
|
|
| Net book value of capitalized software |
1,100,000,000
|
819,000,000
|
|
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| Fuel card obligation |
736,000,000
|
1,075,000,000
|
|
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| Advertising expense |
$ 288,000,000
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$ 267,000,000
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$ 273,000,000
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| Revenue from flights to and from China historically as a percent of revenue |
2.00%
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| Fuel Card Obligation |
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| Summary of Significant Accounting Policies [Line Items] |
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| Purchasing card maximum limit |
$ 1,100,000,000
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| Minimum |
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| Summary of Significant Accounting Policies [Line Items] |
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| Spare parts, estimated residual value (percent) |
5.00%
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| Maximum |
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| Summary of Significant Accounting Policies [Line Items] |
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| Spare parts, estimated residual value (percent) |
10.00%
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| Software and software development costs | Minimum |
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| Summary of Significant Accounting Policies [Line Items] |
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| Estimated useful life |
3 years
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| Software and software development costs | Maximum |
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| Summary of Significant Accounting Policies [Line Items] |
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| Estimated useful life |
10 years
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