Interest Cost Components (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Amount charged to expense	$ 24	$ 378	$ 496	$ 499
Amount capitalized		23	22	32
Interest costs		$ 401	$ 518	$ 531