Revenue Recognition - Receivables and Contract Liabilities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) term
Disaggregation of Revenue [Line Items]
Total	$ 707
Less than 1 year	111
Years 2 to 3	220
Years 4 to 5	220
More than 5 years	$ 156
Transportation Services Operating Leases, Five Year Terms
Disaggregation of Revenue [Line Items]
Initial term	10 years
Number of additional terms | term	2
Additional term	5 years
Transportation Services Operating Leases, One Year Terms
Disaggregation of Revenue [Line Items]
Number of additional terms | term	10
Additional term	1 year
Transportation Services Operating Leases
Disaggregation of Revenue [Line Items]
Initial term	10 years
Transportation Services Operating Leases Amended
Disaggregation of Revenue [Line Items]
Additional term	14 months