Fair Value Measurements - Measured on Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Fuel derivatives:
Option contracts	$ 353	$ 526
Fair Value, Measurements, Recurring
Assets
Treasury bills	2,827	2,226
Fuel derivatives:
Interest rate derivatives (see Note 3)	14	14
Equity Securities	255	235
Total assets	12,787	13,053
Fair Value, Measurements, Recurring | Options Contracts
Fuel derivatives:
Option contracts	339	512
Fair Value, Measurements, Recurring | Commodity Option
Liabilities
Liabilities	23
Fair Value, Measurements, Recurring | Certificates of deposit
Assets
Investments	194	124
Fair Value, Measurements, Recurring | Time deposits
Assets
Investments		450
Fair Value, Measurements, Recurring | Cash Equivalents
Assets
Cash equivalents	8,702	9,040
Fair Value, Measurements, Recurring | Commercial paper
Assets
Cash equivalents	134	179
Fair Value, Measurements, Recurring | Certificates of deposit
Assets
Cash equivalents	22	23
Fair Value, Measurements, Recurring | Time deposits
Assets
Cash equivalents	300	250
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Treasury bills	2,827	2,226
Fuel derivatives:
Interest rate derivatives (see Note 3)	0	0
Equity Securities	255	235
Total assets	11,784	11,501
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Options Contracts
Fuel derivatives:
Option contracts	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Commodity Option
Liabilities
Liabilities	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Certificates of deposit
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Time deposits
Assets
Investments		0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Cash Equivalents
Assets
Cash equivalents	8,702	9,040
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Commercial paper
Assets
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Certificates of deposit
Assets
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Time deposits
Assets
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets
Treasury bills	0	0
Fuel derivatives:
Interest rate derivatives (see Note 3)	14	14
Equity Securities	0	0
Total assets	664	1,040
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Options Contracts
Fuel derivatives:
Option contracts	0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Commodity Option
Liabilities
Liabilities	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Certificates of deposit
Assets
Investments	194	124
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Time deposits
Assets
Investments		450
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Cash Equivalents
Assets
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Commercial paper
Assets
Cash equivalents	134	179
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Certificates of deposit
Assets
Cash equivalents	22	23
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Time deposits
Assets
Cash equivalents	300	250
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets
Treasury bills	0	0
Fuel derivatives:
Interest rate derivatives (see Note 3)	0	0
Equity Securities	0	0
Total assets	339	512
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Options Contracts
Fuel derivatives:
Option contracts	339	512
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Commodity Option
Liabilities
Liabilities	23
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Certificates of deposit
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Time deposits
Assets
Investments		0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Cash Equivalents
Assets
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Commercial paper
Assets
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Certificates of deposit
Assets
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Time deposits
Assets
Cash equivalents	$ 0	$ 0