Commitments and Contingencies - Representations and Warranties Obligations and Corporate Guarantees (Details) - USD ($) $ in Billions	Sep. 30, 2019	Dec. 31, 2018
Representations and Warranties Obligations and Corporate Guarantees
Loss Contingencies [Line Items]
Reserve for representations and warranties and corporate guarantees	$ 1.8	$ 2.0

Amount of loss contingency liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

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