Fair Value (Narrative) (Details) - USD ($) $ in Billions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Indirect Investments - Estimated remaining liquidation period	12 years
Carrying value of FHLB and FRB stock	$ 1.6	$ 1.8

Remaining period of expected liquidation by investee of underlying asset of investment measured at net asset value per share or unit. In 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=SL6742756-110258

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration