Loans and finance receivables - Narrative (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregated carrying value	$ 24,664	$ 22,065
Term Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregated carrying value	1,900	1,900
Term Loan [Member] \| Alleghany Corporation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregated carrying value	450
Seritage Growth Properties [Member] \| Term Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregated carrying value	$ 1,000	$ 1,400
Manufactured and Site-built Home Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of loan balances considered to be current as to payment status	96.00%

Amortized cost, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

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