Summary of Significant Accounting Policies - Capitalized Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies
Total interest costs	$ 485	$ 400	$ 383
Total capitalized interest costs	$ 21	$ 16	$ 15