Revenue - Operating Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Operating revenue	$ 3,221	$ 7,979
Domestic (U.S. and Canada)
Disaggregation of Revenue [Line Items]
Operating revenue	2,111	5,078
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	410	1,215
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	308	806
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	$ 392	$ 880

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details