Fair Value Measurements - Book Values and Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Book Values
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Short-term debt	$ 221	$ 226
Current maturities of long-term debt and finance lease obligations	315	315
Long-term debt and finance lease obligations	5,996	4,809
Fair values
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Short-term debt	221	226
Current maturities of long-term debt and finance lease obligations	315	315
Long-term debt and finance lease obligations	$ 6,324	$ 5,156