Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Footnote Information) (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Abstract]
Fair value of securities purchased under agreements to resell	$ 221,000,000	$ 232,000,000
Securities received as collateral, amount repledged and sold	$ 0	$ 0

The fair value of collateral received that has been sold or re-pledged and is owed to the debtor (transferor) upon settlement of the related contractual obligation under which it was received.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Name:	us-gaap_SecuritiesReceivedAsCollateralAmountRepledgedAndSold
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration