Summary of Significant Accounting Policies - Investments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Other investments	$ 2	$ 62
Colonial
Schedule of Equity Method Investments [Line Items]
Ownership	16.125%	6.00%
Other investments	$ 0	$ 11
Explorer
Schedule of Equity Method Investments [Line Items]
Ownership	38.59%	12.62%
Other investments	$ 0	$ 49
Cleopatra
Schedule of Equity Method Investments [Line Items]
Ownership	1.00%	1.00%
Other investments	$ 2	$ 2