Supplemental Financial Information - Other Assets (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Other Assets [Abstract]
Derivative contracts	$ 175	$ 136
Intangible assets	410	413
Capital lease receivable	72	76
Non-current prepaid maintenance	130	5
Other	172	156
Other assets	$ 959	$ 786