Supplemental Financial Information - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Supplemental Financial Information Narrative [Abstract]
Aircraft Grounding Charge Prepaid Rent	$ 15		$ 15
Aircraft grounding charge	$ 63	$ 0	$ 63	$ 0