Summary of Significant Accounting Policies - Recently Adopted Accounting Policies Narrative (Details) - USD ($) $ in Millions	Jan. 01, 2019	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect on retained earnings	$ 6	$ (34)
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect on retained earnings	$ 6

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

No definition available.

Name:	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant