Guarantor Financial Statement Information - Narrative (Details) $ in Millions	Mar. 31, 2019 USD ($) subsidiary	Dec. 31, 2018 USD ($)
Condensed Financial Statements, Captions [Line Items]
Ownership percentage	100.00%
Number of subsidiaries as guarantors of unsecured debt | subsidiary	3
Unsecured Senior Notes
Condensed Financial Statements, Captions [Line Items]
Unsecured debt	$ 2,498	$ 2,498
6.500% interest rate payable semi-annually, due July 2021 | Unsecured Senior Notes
Condensed Financial Statements, Captions [Line Items]
Interest rate	6.50%
Unsecured debt	$ 592	592
6.500% interest rate payable semi-annually, due June 2022 | Unsecured Senior Notes
Condensed Financial Statements, Captions [Line Items]
Interest rate	6.50%
Unsecured debt	$ 206	$ 206