Investments - Additional Info (Details) $ in Millions	1 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Summary of Investment Holdings [Line Items]
Number of mortgage-backed securities		180	163
Par value of mortgage-backed securities pledged to FRB \| $		$ 888	$ 815
Vertical risk retention interest	5.00%	5.00%
Mortgage-backed securities
Summary of Investment Holdings [Line Items]
Number of government sponsored securities with unrealized losses		60	14

Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant