Commitments, Contingencies and Other Items - Other Commitments (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Amount outstanding under letters of credit or other similar obligations	$ 32	$ 32
Collateralized by cash, that is reflected on the consolidated balance sheets as restricted cash	$ 26	$ 26

The value of the collateral (typically cash) that the entity receives in a financing transaction in exchange for securities lent. This item represents a liability in the financial statements of the lender of the securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 25
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109249708&loc=d3e113275-111724

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(A)(ii))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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