Fair Value Measurements - Book Values and Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Book Values
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Short-term debt	$ 0	$ 226
Current maturities of long-term debt and finance lease obligations	727	315
Long-term debt and finance lease obligations	5,760	4,809
Fair values
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Short-term debt	0	226
Current maturities of long-term debt and finance lease obligations	732	315
Long-term debt and finance lease obligations	$ 6,472	$ 5,156