Loans, Lending Commitments and Allowance for Credit Losses - Troubled Debt Restructurings (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Troubled Debt Restructurings
Loans	$ 46	$ 38
Lending commitments	49	45
Allowance for loan losses and lending commitments	$ 5	$ 4

Amount of financing receivable modified as troubled debt restructuring.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18845-111554

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