Fair Value Measurements, Other Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financial assets:
Cash and cash equivalents, at carrying amount	$ 2,033	$ 2,982
Financial liabilities:
Debt (excluding finance leases), at carrying amount	8,710	8,503
Fair Value, Inputs, Level 1 [Member]
Financial assets:
Cash and cash equivalents, at fair value	2,033	2,982
Fair Value, Inputs, Level 2 [Member]
Financial liabilities:
Debt (excluding finance leases), at fair value	$ 10,123	$ 8,986