Intangible Assets - Definite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets
Definite-lived intangible assets, gross carrying value	$ 976	$ 976
Definite-lived intangible assets, accumulated amortization	(862)	(845)
Marketing agreements
Finite-Lived Intangible Assets
Definite-lived intangible assets, gross carrying value	730	730
Definite-lived intangible assets, accumulated amortization	(687)	(677)
Contracts
Finite-Lived Intangible Assets
Definite-lived intangible assets, gross carrying value	193	193
Definite-lived intangible assets, accumulated amortization	(122)	(115)
Other
Finite-Lived Intangible Assets
Definite-lived intangible assets, gross carrying value	53	53
Definite-lived intangible assets, accumulated amortization	$ (53)	$ (53)