Debt - Fair Value of Debt (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Fair value of debt	$ 6,052	$ 5,580
Level 1
Debt Instrument [Line Items]
Fair value of debt	2,981	3,190
Level 2
Debt Instrument [Line Items]
Fair value of debt	$ 3,071	$ 2,390