Debt Variable Interest Entities - Leases (Details) $ in Millions	Dec. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Future minimum lease payments	$ 2,721	[1]
Variable Interest Entity, Not Primary Beneficiary | Equipment
Operating Leased Assets [Line Items]
Future minimum lease payments	$ 1,500

[1] Excludes leases having non-cancelable lease terms of less than one year and per diem leases.