Condensed Financial Information of the Parent Company - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Interest paid	$ 892	$ 598	$ 429
Key [Member]
Condensed Financial Statements, Captions [Line Items]
Interest paid	$ 131	$ 120	$ 114