Leases - Operating Lease Assets and Liabilities in the Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Right-of-use assets classified in Other noncurrent assets	$ 277
Current portion of lease liabilities classified in Other current liabilities	77
Long-term portion of lease liabilities classified in Other noncurrent liabilities and deferred credits	211
Total lease liabilities	$ 288