Debt - Fair Value of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Fair value of debt	$ 5,580	$ 4,305
Level 1
Debt Instrument [Line Items]
Fair value of debt	3,190	2,020
Level 2
Debt Instrument [Line Items]
Fair value of debt	$ 2,390	$ 2,285