Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Schedule of Cash Flow, Supplemental Disclosures [Line Items]
Interest paid	$ 199	$ 182
Property and equipment acquired	105
Foreign and State
Schedule of Cash Flow, Supplemental Disclosures [Line Items]
Income taxes paid	544	545
Domestic
Schedule of Cash Flow, Supplemental Disclosures [Line Items]
Tax refunds	$ 2	$ 2