Fair Value Measurements, Other Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financial assets:
Cash and cash equivalents, at carrying amount	$ 2,982	$ 5,850	$ 4,816	$ 4,114
Financial liabilities:
Debt (excluding capital leases), at carrying amount	8,503	8,310
Fair Value, Inputs, Level 1 [Member]
Financial assets:
Cash and cash equivalents, at fair value	2,982	5,850
Fair Value, Inputs, Level 2 [Member]
Financial liabilities:
Debt (excluding capital leases), at fair value	$ 8,986	$ 9,795