Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 18,283	$ 11,269	$ 2,762
Restricted cash	37	255	0
Other assets:
Restricted cash	213	218	106
Total cash, cash equivalents and restricted cash shown in the statement of consolidated cash flows	18,533	11,742	2,868	$ 1,799
United Airlines, Inc.
Current assets:
Cash and cash equivalents	18,283	11,269	2,756
Restricted cash	37	255	0
Other assets:
Restricted cash	213	218	106
Total cash, cash equivalents and restricted cash shown in the statement of consolidated cash flows	$ 18,533	$ 11,742	$ 2,862	$ 1,793